Why did thousands of chinese protesters gather in tiananmen square in 1989

The Chinese were protesting the Communist dictatorship. I assume they wanted a democratic government where the people had the right to vote. The protest was successfully suppressed by the Chinese government.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.

c, because the american revolution was from 1765 to 1783.