America does not have a will to empire. A traditional empire at least. It's not for any high-minded reasons, either. Even though many would claim otherwise.
Every time that countries offered themselves up for annexation (sometimes more willingly than others), efforts stalled in the US Congress. Lots of industry lobbies did not want their products to have to compete with those from the possible new territory. Anti-immigrant activists did not want a new wave of the "others" arriving from overseas. Unions did not want more low-skill workers driving down wages for those that they already represented. Before the civil war, every question of free vs slave state was one of the many the US Congress had to get over before it annexed new territory.
No wonder so many attempts to include new states into the union failed: Puerto Rico, Cuba, Philippines, Dominican Republic, etc. Others failed initially, but were eventually granted statehood: Hawaii and Texas.
In my Texas history class in 7th grade, we were taught the proud history of our Republic. How we bravely broke off and triumphed in our revolution against tyranny. Texans wanted to be free. Well... as one might imagine, that was only half the story... Texans wanted to be free English-speaking Protestants who didn't want to pay taxes to a Spanish-speaking Catholic empire-state. Oh, and they wanted to be able to own slaves. That was a big kicker. The freedom people loving of Texas wanted the right to own other people.
Texas didn't want to be an independent Republic either. Independence was forced upon it as Congress could not agree on what to do with the place. It took almost 15 years of negotiations before Texas was finally given statehood. And it was done so mainly to provoke a war with Mexico to take over more sparsely populated territory to the West. Gold was just discovered in California. So if taking Texas meant getting California, then so be it.
The conclusion of all this is that America's lack of will to build a traditional empire is founded on its great democratic tradition. As a democracy, people were able to lobby their congressmen with their anti-immigrant , anti-Catholic, and protectionist sentiments. Populist positions. But America is willing to overcome these prejudices if valuable natural resources - mainly Gold and Oil - are at stake. American foreign policy is not built around a will to traditional empire, but rather a liberal one.
Instead, America has a will to enforce international business contracts and free trade.
Free trade allows America to extract natural resources from countries by simply purchasing them on the open market. No need to actually control the people and government. That would be much more expensive endeavor as the Europeans learned. Let them bear the moral and monetary burden of governing themselves - even if it is not exactly the most democratic in fashion.
Most, but not all, American overseas adventures were attempts at enforcing contracts. Either collection on debts that were lent out to other nations or protecting US companies from nationalization that invested in extraction of vital natural resources at a pre-determined price. Needless to say, most of these contracts (and treaties, for that matter) were written in a very one-sided manner, if possible.