Answer:
Domestically, the United States ensures the safety of its citizens, and will without hesitation initiate a military intervention on behalf of its citizens. This is due to the fact that they are its first and foremost ally.
For situations like this, the american constitution has made provision for the importance of its citizens above every other. Externally, the united states has several allies with whom it has made pact. This pacts can cover from military support when need be, to providing economic and social support. The major allies of the united states are within Nato, formed during the cold war era to bolster america's chances of winning in the case of a war outbreak between the united states and the USSR. Till date, america has kept its end of the bargain by contributing financial and military efforts, even going as far as shouldering the major responsibilities of NATO.