In recent years the U.S. has gathered such alliances. We have committed not only to support our "allies" in conflict situations, but also to provide them with weapons that make combat an attractive choice. We have subscribed to the idea that the enemy of my ally is my enemy. It's a sort of permanent view of how the world is divided.
Prior to WWII this methodology did not exist. Nations made alliances with other nations based upon the particular situation and estimates of individual and world interests. Coalitions changed. For example, throughout history most countries had varying alliances. In WWI Italy joined with Britain and France against Germany; in WWII Italy allied with Germany. In WWII Russia was allied with the U.S., Britain and France; in the following Cold War years Russia, for political and other reasons, became "the enemy."
During these years the U.S. entered the frays slowly and reluctantly, depending upon our appraisal of the situation and the need for U.S. assistance. We were not involved ipso facto through long-standing alliances that required us to join the fighting. We had the opportunity to thoroughly debate our involvement
But U.S. policy has changed. We have come to adopt the thinking of "permanent friends" and "permanent enemies." We have a professional military and a military arsenal strong enough to defend us and our friends at a moment's notice. We have forgotten our first president's advice to beware of permanent alliances. George Washington was aware that situations change, and our interests are not always the same as those of another nation. It is not in our interest to be so committed to another nation that we fight their wars. Nations should be responsible for their own defense.
The world has changed, of course, in the 21st century. Small groups and individuals, as well as nations, have the motives and the resources to initiate violent actions. It is more important than ever for the U.S. to weigh alternatives carefully, to seek nonviolent solutions to problems, to make friends not enemies.