user11826: Government army need to follow orders by Government. In the war, army has to kill the terrorists. That is the nature of war and defeating terrorists is their job.
So is it consider as  bad karma?
I know some army mens who killed more than 100 terrorists. What will happen for them in next life?

user471: In the Yodhajiva Sutta, we find that the warrior who has the intention to kill and does exert himself to kill, would be reborn in hell or as an animal:

When a warrior strives & exerts himself in battle, his mind is already
  seized, debased, & misdirected by the thought: 'May these beings be
  struck down or slaughtered or annihilated or destroyed. May they not
  exist.' If others then strike him down & slay him while he is thus
  striving & exerting himself in battle, then with the breakup of the
  body, after death, he is reborn in the hell called the realm of those
  slain in battle. But if he holds such a view as this: 'When a warrior
  strives & exerts himself in battle, if others then strike him down &
  slay him while he is striving & exerting himself in battle, then with
  the breakup of the body, after death, he is reborn in the company of
  devas slain in battle,' that is his wrong view. Now, there are two
  destinations for a person with wrong view, I tell you: either hell or
  the animal womb."

On the other hand, protection is OK (from DN16):

"What have you heard, Ananda: do the Vajjis duly protect and guard the
  arahats, so that those who have not come to the realm yet might do so,
  and those who have already come might live there in peace?"
"I have heard, Lord, that they do."
"So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline."

In Buddhism, kamma is based on intention. What was the intention of exemplary Buddhist King Asoka? We can see this from The Edicts of King Asoka:

Beloved-of-the-Gods speaks: thus This Dhamma edict was written
  twenty-six years after my coronation. Happiness in this world and the
  next is difficult to obtain without much love for the Dhamma, much
  self-examination, much respect, much fear (of evil), and much
  enthusiasm. But through my instruction this regard for Dhamma and love
  of Dhamma has grown day by day, and will continue to grow. And my
  officers of high, low and middle rank are practicing and conforming to
  Dhamma, and are capable of inspiring others to do the same. Mahamatras
  in border areas are doing the same. And these are my instructions:
  to protect with Dhamma, to make happiness through Dhamma and to guard with Dhamma.
All men are my children. What I desire for my own children, and I
  desire their welfare and happiness both in this world and the next,
  that I desire for all men. You do not understand to what extent I
  desire this, and if some of you do understand, you do not understand
  the full extent of my desire.
Truly, I consider the welfare of all to be my duty, and the root of
  this is exertion and the prompt despatch of business. There is no
  better work than promoting the welfare of all the people and whatever
  efforts I am making is to repay the debt I owe to all beings to assure
  their happiness in this life, and attain heaven in the next.
Therefore this Dhamma edict has been written to last long and that my
  sons, grandsons and great-grandsons might act in conformity with it
  for the welfare of the world. However, this is difficult to do without
  great exertion.


user12588: One of the five basic Buddhist precept says:
“abstain from harming living beings”
No matter if they are terrorists or monks. Killing is wrong.
I suggest not to worry about what will happen to killers on their next lives, but rather, on the current one. They are getting away from the path of virtue and kindness.

user10100: Whole life killing attention is bad kamma, no exception. Even though that bad kamma causes some little good effects. Because killing directly causes bad effect, such as unwholesome mind factors, life's death, etc. Also side effects of killing cause many variant bad effects, too, such as vengeance. Actually, only one killing causes more than ten enemies' vengeance: parents' vengeance, brothers', sisters', aunts', uncles', grandpas', grandmas', partners', sons', daughters', friends', etc.
For the example: 
Some americans thought bin laden killing can causes terrorism's cessation. But the fact appearing that we still face the terrorism.
So, buddha said:

Na hi verena verni, sammantīdha kudācanaṃ
Unwholesome (akusalakammapatha, such as vengeance) never ceased by the unwholesome (akusalakammapatha, such as vengeance).

For the last question:

I know some army mens who killed more than 100 terrorists. What will happen for them in next life?

It is answered by Nirayasuttaṃ:

018.03. Bhikkhus, endowed with five things the lay disciple is in hell as though led and lain. What five?
Destroying living things, taking the not given, misbehaving in sexual
  desires, telling lies and taking intoxicated and brewed drinks
  Bhikkhus, endowed with these five things the lay disciple is in hell
  as though led and lain there.
Bhikkhus, endowed with five things the lay disciple is in heaven as
  though led and lain there. What five?
Abstaining, from destroying living things, taking the not given,
  misbehaving in sexual desires, telling lies and taking intoxicated and
  brewed drinks Bhikkhus, endowed with these five things the lay
  disciple is in heaven as though led and lain there.


11826: <p>Government army need to follow orders by Government. In the war, army has to kill the terrorists. That is the nature of war and defeating terrorists is their job.</p>

<p>So is it consider as  bad karma?</p>

<p>I know some army mens who killed more than 100 terrorists. What will happen for them in next life?</p>
 471: <p>In the <a href="https://www.accesstoinsight.org/tipitaka/sn/sn42/sn42.003.than.html" rel="nofollow noreferrer">Yodhajiva Sutta</a>, we find that the warrior who has the intention to kill and does exert himself to kill, would be reborn in hell or as an animal:</p>

<blockquote>
  <p>When a warrior strives &amp; exerts himself in battle, his mind is already
  seized, debased, &amp; misdirected by the thought: 'May these beings be
  struck down or slaughtered or annihilated or destroyed. May they not
  exist.' If others then strike him down &amp; slay him while he is thus
  striving &amp; exerting himself in battle, then with the breakup of the
  body, after death, he is reborn in the hell called the realm of those
  slain in battle. But if he holds such a view as this: 'When a warrior
  strives &amp; exerts himself in battle, if others then strike him down &amp;
  slay him while he is striving &amp; exerting himself in battle, then with
  the breakup of the body, after death, he is reborn in the company of
  devas slain in battle,' that is his wrong view. Now, there are two
  destinations for a person with wrong view, I tell you: either hell or
  the animal womb."</p>
</blockquote>

<p>On the other hand, protection is OK (from <a href="https://www.accesstoinsight.org/tipitaka/dn/dn.16.1-6.vaji.html" rel="nofollow noreferrer">DN16</a>):</p>

<blockquote>
  <p>"What have you heard, Ananda: do the Vajjis duly protect and guard the
  arahats, so that those who have not come to the realm yet might do so,
  and those who have already come might live there in peace?"</p>
  
  <p>"I have heard, Lord, that they do."</p>
  
  <p>"So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline."</p>
</blockquote>

<p>In Buddhism, kamma is based on intention. What was the intention of exemplary Buddhist King Asoka? We can see this from <a href="https://www.accesstoinsight.org/lib/authors/dhammika/wheel386.html" rel="nofollow noreferrer">The Edicts of King Asoka</a>:</p>

<blockquote>
  <p>Beloved-of-the-Gods speaks: thus This Dhamma edict was written
  twenty-six years after my coronation. Happiness in this world and the
  next is difficult to obtain without much love for the Dhamma, much
  self-examination, much respect, much fear (of evil), and much
  enthusiasm. But through my instruction this regard for Dhamma and love
  of Dhamma has grown day by day, and will continue to grow. And my
  officers of high, low and middle rank are practicing and conforming to
  Dhamma, and are capable of inspiring others to do the same. Mahamatras
  in border areas are doing the same. And these are my instructions:
  <strong>to protect with Dhamma</strong>, to make happiness through Dhamma and <strong>to guard with Dhamma</strong>.</p>
  
  <p><strong>All men are my children. What I desire for my own children, and I
  desire their welfare and happiness both in this world and the next,
  that I desire for all men.</strong> You do not understand to what extent I
  desire this, and if some of you do understand, you do not understand
  the full extent of my desire.</p>
  
  <p><strong>Truly, I consider the welfare of all to be my duty</strong>, and the root of
  this is exertion and the prompt despatch of business. There is no
  better work than promoting the welfare of all the people and whatever
  efforts I am making is to repay the debt I owe to all beings to assure
  their happiness in this life, and attain heaven in the next.</p>
  
  <p>Therefore this Dhamma edict has been written to last long and that my
  sons, grandsons and great-grandsons might act in conformity with it
  for the welfare of the world. However, this is difficult to do without
  great exertion.</p>
</blockquote>
 12588: <p>One of the five basic Buddhist precept says:</p>

<p>“abstain from harming living beings”</p>

<p>No matter if they are terrorists or monks. Killing is wrong.</p>

<p>I suggest not to worry about what will happen to killers on their next lives, but rather, on the current one. They are getting away from the path of virtue and kindness.</p>
 10100: <p>Whole life killing attention is bad kamma, no exception. Even though that bad kamma causes <strong>some little</strong> good effects. Because killing directly causes bad effect, such as unwholesome mind factors, life's death, etc. Also side effects of killing cause many variant bad effects, too, such as vengeance. Actually, only one killing causes more than ten enemies' vengeance: parents' vengeance, brothers', sisters', aunts', uncles', grandpas', grandmas', partners', sons', daughters', friends', etc.</p>

<p>For the example: </p>

<p>Some americans thought bin laden killing can causes terrorism's cessation. But the fact appearing that we still face the terrorism.</p>

<p>So, buddha said:</p>

<blockquote>
  <p><em>Na hi verena verni, sammantīdha kudācanaṃ</em></p>
  
  <p>Unwholesome (akusalakammapatha, such as vengeance) never ceased by the unwholesome (akusalakammapatha, such as vengeance).</p>
</blockquote>

<p>For the last question:</p>

<blockquote>
  <p>I know some army mens who killed more than 100 terrorists. What will happen for them in next life?</p>
</blockquote>

<p>It is answered by <a href="http://www.84000.org/tipitaka/pitaka_item/r.php?B=22&amp;A=4756&amp;w=%E3%B9%B9%C3%A1&amp;eng=metta_e" rel="nofollow noreferrer">Nirayasuttaṃ</a>:</p>

<blockquote>
  <p>018.03. Bhikkhus, endowed with five things the lay disciple is in hell as though led and lain. What five?</p>
  
  <p>Destroying living things, taking the not given, misbehaving in sexual
  desires, telling lies and taking intoxicated and brewed drinks
  Bhikkhus, endowed with these five things the lay disciple is in hell
  as though led and lain there.</p>
  
  <p>Bhikkhus, endowed with five things the lay disciple is in heaven as
  though led and lain there. What five?</p>
  
  <p>Abstaining, from destroying living things, taking the not given,
  misbehaving in sexual desires, telling lies and taking intoxicated and
  brewed drinks Bhikkhus, endowed with these five things the lay
  disciple is in heaven as though led and lain there.</p>
</blockquote>
