Why does wickham want revenge on darcy?

Mr. Darcy explains that after both his and Mr. Wickham's fathers pass away, it is left to Mr. Darcy to uphold the late Mr. Darcy's will and promote Mr. Wickham in his profession; ie: helping Wickham to find a location where he could take up his living in the religious order. However, Wickham comes to Darcy and explains that he has no plans to be a clergyman, but instead plans to study the law.

Darcy realized his irrational and wild behavior and withheld the family fortune, leaving Wickham with less money than he wanted. Darcy also prevented Wickham from marrying his sister, also denying him familial wealth.

From mexican american war , us gained new mexico.