8They Provide Much Of The Food For Westeros
If one were to have a choice of any region of Westeros to maintain a kingdom, The Reach would likely be the top choice for many.
Known for it’s rich and bountiful lands, The Reach is the most populous of the Seven Kingdoms, yet it
produces more food than its inhabitants can consume. A real life equivalent would be the breadbasket of the United States, with areas consisting of fertile farmland for hundreds of kilometers in any direction.
Naturally, this means that they are the main exporters of food throughout Westeros. In times of peace, they maintain a complex but efficient network of distribution that can be as effective a weapon as any blade in times of war.
When the Tyrells married into the Royal Family through Margery being betrothed to Joffrey, the Tyrells reopened their supply lines to their former enemies and brought with them a much needed abundance of food for the starving capital.
This doubled as a message to the Lannisters-- we can save you, but we can also starve you. The Lannisters treaded lightly thereafter.