What caused the massacre of protesters in China's Tiananmen Square in
1989?

i would say embarrassment because their country looked to be shambles, also the government not wanting to affect daily life.

Explanation:

Even so, feeling the demonstrations needed to be curtailed, the Chinese government declared martial law on May 20 and 250,000 troops entered Beijing.

By the end of May more than one million protesters had gathered in Tiananmen Square. They held daily marches and vigils, and images of the events were transmitted by media organizations to audiences in the United States and Europe.

The communist party deemed the protests against government policies as a political threat, and took military action.

Explanation:

A. P. E. X.

the roman empire began to fall