How did Muhammad Ghori benefit from Mahmud of Ghazni's death?

Mahmud of Ghazni ruled from 997 to 1030 and extended control over parts of Central Asia. He had defeated the ruler of Ghor and had made him his vassal. After Mahmud’s death, however, the Ghaznavids become weak. Taking advantage of this, Muhammad Ghori became independent. He also annexed all Ghaznavid territories. He took the city of Ghazni in 1173 to avenge the death of his ancestor Muhammad ibn Suri at the hands of Mahmud of Ghazni.