This is why the US military is partnered with all the Middle East democracies, like the one in Bahrain, or the one in UAE, or the one in Qatar…
this is pure propaganda and is completely false statement, not grounded in reality. US has no problem protecting despotic autocracies like the Pinochet's junta in Chile or Saudi Arabian theocratic monarchy (a birthplace of islamic wahhabism).
The actual goal of military is to protect the status of USD as a global reserve currency and ensure all important nations are its vassals, fully subordinate to the US government.
The underlying reason is America is printing trillions of dollars out of thin air, not backed by anything, other than the threat from US military, so vassal states keep recycling their earned surplus currency into USD bonds and treasuries
The US entered World War II in the pacific after Pearl Harbor and in Europe after Germany declared war.
Before those 2 events, there was still a strong isolationist contingent in the US.
Yes, there were isolationists, but there weren't enough to change the fact that fascist/communist victories in Europe would be bad for America. The neoliberal thing where we support liberal democracies is an evolution of the Monroe doctrine, because we've recognized for a long time that the best path forward for America is free trade and interdependency with other like-minded countries.
How is US defending liberal democracy?
So far they've killed 3,000+ Iranians. 110k+ causalities in IRAQ and Afghanistan.. don't even get me started on Vietnam.