Working together, the branches of government do have the power to end war, clean up the environment, get our infrastructure working again, all those good things you mentioned.  The really sad truth about the past eight years is that the legislative branch did nothing but obstruct the ideas which would improved the country.  
Too many in power regarded Obama as an upstart, someone of the wrong color to be elected to such high office.  They never thought it could happen to their comfortable little world, and when it did they set about denying it and find a way to make it not happen.  
Remember the ominous undertones of "Take our country back!"?  Prominent members of Congress treated their new president with veiled derision, as someone who should be using the servants' entrance, and determined to hold him to one term.  Under those leaders, Congress fought against nearly anything Obama proposed.  What a terrific waste of time and effort.