How was the qing dynasty replaced by a republic?

The Nationalist government that was struggling was replaced by the Republic. The Chinese were dealing with all their problems, a weak government, and also influence and attacks from the outside all at once. People were involved in Chinese politics at the same all had different opinion. Some said they must get rid of dynastic system, some say the Manchus, some say it should be constitutional, some say emperor, etc. The only agreement China could come up with was the need for a revolution, not a reform. Sun Yatsen introduced the idea of the Republic but it did not have much of a positive effect on China's issues with internal and/or external factors.