There is no such thing as a quick and easy war. You start a war, expect it to last years or decades.
The stupid shit the US has done since the 50s, have alienated the Muslim world to the west. Dropping bombs on terrorists and their families helped the muslim proproganda against the US.
The war in Ukraine is touchy; because as soon as NATO forces (including the US) engage with Russian troops, the Russians will use nuclear weapons.
As for Taiwan, if China invades, expect US force to bomb all chip factories so they don't fall into Chinese hands. If a war does start out, the US will need a supply of every thing the Chinese make, from somewhere else, or produce it themselves.
As for war strategies there are some countries that think medieval, some WW1/WW2 strategies, some gulf war, some new warefare of drone onslaughts. The weapons of the new battlefield will be lasers, hypersonic missiles, drone swarms, and railguns (hyper velocity bullets).
The side that will win will be the side that has its industry deep underground and impenetrable to missiles and bombs. lets put that number under 500 ft of ground, with triple reenforced concrete. If you haven't done this since the 1950s then you are 80 years behind the times.
China will take over as the premier country over the US due to its uprise in its economy and influence in 2nd and 3rd world countries. Countries the Western world didn't invest in if those countries didn 't have resources.