@Lord Varys in another thread quickly mentioned that the Free Cities might be drawn into the war of Westeros or have an important role to play. I tend to agree. These are my thoughts.
Bravos is throwing its (financial) weight behind Stannis, going to great lengths to reach him and lend him additional money. For all they know they are supporting the losing side. Surely the Lannister faction angered them but I guess there is more than that. They are putting heavy economic pressure on the whol
1) Because she can do it. After Vaes Dothrak she will have the largest army in the world.
2) Because geographically she needs to do it. If she wants to head West, she needs to pass through some of these cities. In particular Volantis is unavoidable. Armies need food and water and plunder. Ships needs to be resupplied and repaired. And she needs to finish the slave market once for all, otherwise she will leave behind a multitude of Astapors.
3) Because there are hanging plots that need