The Chinese civil war never officially ended. There was no agreement whatsoever, and the ROC never declared itself as separate, etc. Taiwan is simply a province within the ROC, and the ROC still consists of the mainland. That's what the ROC constitution states.
Here is a ChatGPT response to you because I wont bother with kneejerk responses:
In the last 100 years, the United States has been involved in several military invasions and interventions in various countries. Some notable examples include:
Mexico (1914) - U.S. forces occupied Veracruz.
Haiti (1915-1934) - U.S. Marines occupied Haiti to stabilize the country.
Dominican Republic (1916-1924) - U.S. intervention to restore order and protect American interests.
Korea (1950-1953) - U.S. involvement in the Korean War, supporting South Korea against North Korea.
Vietnam (1955-1975) - Extensive military involvement in the Vietnam War.
Grenada (1983) - U.S. invasion to overthrow the government and restore order.
Panama (1989) - Operation Just Cause to depose Manuel Noriega.
Iraq (2003) - Invasion to overthrow Saddam Hussein, followed by a prolonged military presence.
Afghanistan (2001-2021) - Response to the 9/11 attacks, targeting the Taliban and al-Qaeda.
This list highlights significant military actions but is not exhaustive, as the U.S. has also conducted numerous smaller operations, interventions, and covert actions in various countries over the years.
Invading and annexing isn't some weird thing no one usually does.
Taiwan is the product of a recent civil war.