Why did the union want to capture Sabine pass and Brownsville?

The Union aimed to capture Sabine Pass and Brownsville to secure vital access to Texas' Gulf Coast, which was crucial for controlling supply routes and blockading Confederate trade. Capturing these locations would also disrupt Confederate logistics and troop movements, potentially weakening their overall military capacity. Additionally, controlling this area would enhance Union influence in the region and support broader strategies to reclaim Texas and reduce Confederate territorial claims.