What angered the people in the colonies mexican independence day?

The Mexico gained its Independence from Spanish colonial rule on 27th September 1821. But She celebrates her Independence every year on 16 September as it was the day when the Maxican rebel leader Hidalgo  made a cry for Independence.

Oppressive colonial rule, heavy taxation, economic downturn, discrimination with the indigenous population angered the Maxican people which led them to fought for their Independence.

1) union forces launched a surprise attack.

2) more confederate troops arrived by train.

3) union forces retreated.