belgrade paratroopers serbia unite state jump side-by-side north belgrade friday part train tailor bolster tie balkan country nato exercise dub winter 2017 may raise eyebrows moscow want keep serbia slavic orthodox christian ally umbrella worry possible nato expansion balkans also long way 1999 nato bomb yugoslavia policies toward kosovo although european union serbia single large trade partner investor russia control oil gas supply moscow also seek bolster military tie belgrade donation six mig-29 fighter jet serbia one balkan countries 28-member nato hugely unpopular due 1999 bomb campaign alliance troop still deploy kosovo serbia former southern province whose 2008 independence accept belgrade russia china eu members joint exercise take place anyway 100 paratroopers serbian elite brigade u.s. army 173rd airborne brigade land grassy runway small airport near belgrade serbian president aleksandar vucic dub drill part confidence-building activities goal creation cooperation partnerships friendships areas always able boast past vucic tell reporters 2006 serbia maintain military neutrality join nato partnership peace program 2015 sign individual partnership action plan high level cooperation countries aspire join although strive balance moscow west reject call u.s. officials pick side serbia 2017 13 military drill nato members seven u.s. two russia serbian u.s. army paratroopers jump together boost tie