Under capitalism the army is made up of volunteers.
A draft (military conscription) is where the government uses the police power of the state to force citizens to fight in (and die in) wars that the citizens do not agree with. The proper name for such a hideous concept is slavery.
In a capitalist country, there is no draft, in which governments can force their citizens to fight wars.
What will a capitalist country do if it is attacked?
If a capitalist country is attacked it will retaliate and defend itself using the most powerful kind of army possible: a volunteer army of individuals who do not wish to live their lives as slaves.
Doesn't capitalism lead to wars?
As history has shown, the most significant period of world peace was during 19th century predominantly capitalist America. Observe that in the 20th century the world wars were all started by the anti-capitalist collectivist countries.
The policy of a capitalist government to other countries is identical in principle to its policy towards its citizens: the banning of the initiation of force from all relationships.
This same principle applies to non-capitalist statist governments: the policy of a collectivist government towards other nations is identical to its policy towards its citizens: both are sacrificial fodder to the interest of the state or "public good." After all, if a statist government is willing to initiate force within its borders against its people, what principle is there to stop it from initiating force outside its borders? The policy of robbing the wealth of other countries is that of collectivism, and not capitalism, whose only policy is production and trade.
A capitalist country is not a pacifist, and neither is it an aggressor (initiator). If a capitalist country is attacked it will retaliate and defend itself, as it does with any tyrant, brute, and monster, using the most potent kind of army possible: a voluntary army of free men who wish to live their lives as free-men and not as slaves.
What does a capitalist businessman (as opposed to a mixed-economy profiteer) have to gain from wars?
A businessman gains nothing by having his property taxed away to pay for war, only a power-seeking bureaucrat and his cronies ("war profiteers") do. Thus, the businessman in a capitalist country opposes wars. The only men who benefit from wars are those with political pull, who gain their wealth through extortions from their fellow men through the power of government. Whatever these looters are they are not businessmen — they gain their wealth by political favors, and not through competition in the free-market. Their wealth is gained through coercion and extortion of their fellow citizens.
Is capitalism for isolationism or imperialism?
"Isolationist" is a smear term, used against countries who don't wish to interfere in other countries. If the country does interfere it is called "Imperialist". Either way the country — America — is condemned.
Whether America sends its young boys to die off in other countries, or not, should be solely based on America's own self interest — and the interests of those who are risking their lives.
In the Middle East America has a selfish interest: oil. In Kosovo, it has no interest. America does have the moral right to overthrow the present government of Bosnia, as it is not a sovereign nation, as its citizens are not sovereign, i.e., their rights are violated by their own government. However, America has no obligation to overthrow such governments. (As for your views on Hitler, a good argument can be made that America should have let the Nazis and the Soviets go at it, so that the two great slave states of the 20th century would wipe each other out, or at least the victor of this war between Germany and Russia would be so weak as to be easily defeated by the U.S.).
In terms, of improving the situation of countries, like Bosnia, that is primarily a philosophical issue (those countries need a culture founded on individualism, as opposed to a culture founded on collectivism/racism). Sadly, on this issue, America is intellectually bankrupt, as the ideas it exports to other countries tend to be anti-American, Leftist ones, i.e., collectivist ideas that lead to global balkanization.