What led to the Tiananmen Square massacre in China 30 yrs ago?

More than one million pro-democracy protesters occupied Beijing's Tiananmen Square in 1989 and began the largest political demonstration in communist China's history. The demonstrations lasted for six weeks before the Chinese Army was sent in. On June 3, Chinese tanks moved in and troops opened fire, killing and injuring hundreds of unarmed people in and around Tiananmen Square.