I don't think we should pull back to our borders. That is a stupid idea that would disrupt the global balance of power at the expense of the entire western world. Although, it would be funny watching Europe militarize. But we shouldn't go to war to spread democracy or end genocide. We should only consider military or financial intervention when it is in our national interest to do so. Defeating a rising imperialist power and assassinating democratically elected communist leaders are examples of when it's okay to intervene.
Edit: The Greek historian Thucydides said it best, "The strong do what they can, and the weak suffer what they must." The leaders of all states only care about political survival and increasing their power. The US is no exception. The US acts exactly as a political realist would act with the power it has.
Napoleon didn't try to conquer the world. The nobility of Europe was out to get him, and Napoleon was defending France from the constant invasions mounted against him. Whenever a peace settlement was concluded, a new coalition formed while he was resting in Paris. He was more concerned with creating allied buffer states like the Confederation of the Rhine than he was in conquest. Likewise, he didn't conquer Austria, rather he married an Archduchess and required Austria to limit the size of its army. Despite Napoleon's unpopularity with the nobility of Europe, it was because Britain would not relent that the Napoleonic wars continued for as long as they did. Granted, Napoleon had an ego, and he went overkill when he invaded Russia. He should have launched a smaller punitive expedition, and waited until his shipyards finished building his new fleet. With the size of his Empire, he was outproducing Britain, and would have eventually overwhelmed the British Empire
Alexander The Great wasn't a tyrant, lol. He was rather benign as far as a ruler.
Hannibal wasn't a bloodthirsty lunatic out to conquer either. He refused to accept the conditions Rome imposed on Carthage, and he was too gentle after the battle of Cannae. Rather than march on Rome and finish it, he thought the Romans would finally relent and agree to a more sensible settlement. Instead, he wasted his one opportunity to finish Rome in the hope they would agree to peace.