https://thehill.com/opinion/national-security/473468-what-is-that-big-us-military-for-anyhow
There are, roughly speaking, two ways to use a large, modern military force. The first is to enforce international “rules of the road,” guaranteeing freedom of the seas or punishing gross violations of international law and treaties, or keeping the peace by backing up treaties with capabilities. This includes rescuing Kuwait from invasion and occupation by Saddam’s Iraq. It includes retaliating for Syria’s use of chemical weapons. The second is to try to settle other people’s problems. This could include the Vietnam War, 18 years of war in Afghanistan, or centuries-long animosities engendered by 400 years of Turkish anti-Arab colonialism called the Ottoman Empire.
Very roughly speaking.
The historic wars of Europe engendered no American participation; World Wars I and II did, and in the aftermath, keeping Germany under control as well as preventing the further takeover of central Europe by Russia was the basis for NATO. We have no formal alliance with Taiwan or Israel but we operate under the terms of the Taiwan Relations Act and decades of close security cooperation with Israel.
President Donald Trump appears to believe more in the first construct for the use of force and less in the second.
Despite fears that the U.S. might quit NATO — and pretensions by France and Germany that they could field a European military force to replace it — the fact is that under the Trump administration, U.S. spending on NATO has increased and European spending on NATO also has increased.
NATO Secretary General Jens Stoltenberg noted that defense spending across European allies and Canada increased in real terms by 4.6 percent in 2019. “This is unprecedented progress and it is making NATO stronger,” he said. Stoltenberg told reporters in Brussels before the G-7 meetings that the organization’s burden-sharing rules also have changed: “We have now agreed to a new formula for sharing those costs. … The U.S. will pay less. Germany will pay more. So now the U.S. and Germany will pay the same, roughly 16 percent of NATO’s budget.”