Mughals constantly fought against rulers who did not accept their authority. But as the Mughals became powerful, many other rulers, like Rajputs, joined them voluntarily. What was one of the things that many Rajput lords and kings did to get high positions in the Mughal Empire?

Matrimonial alliance.

Explanation:

The Mughals steadily grew into a strong power with its continous warfare with numerous enemies and empires over time. As the empire grew stronger, many smaller kingdoms and rulers surrendered themselves voluntarily to the Mughals. Eventually many Rajput Kings also joined the empire.

One of the most common practice through which the Rajputs secured alliance and high positions in the Mughal Empire was through matrimonial alliance. Many Rajputs gave their daughters in marriage to powerful Mughal families.