His widow, Margery Tyrell, became Robb's bride, and with her came the backing of the Reach in future conflicts. Joffery was beheaded for having ordered the death of Eddard Stark. Therefore, he marched his 35,000 men straight to King's Landing where he knew he would be able to capture Joffery.
Rather than marrying the Frey girl or Jeyne Westerling, Robb decided he needed to marry to secure a larger alliance with one of the Seven Kingdoms in order to solidify indepence for the North after the war.
