Battles over the control of straits are often related to the control of:

trade

Explanation:

The straits are places that are one of the most important when it comes to trade. They are used as part of trade routes, but they are usually the point that connects two major parts of the trade route, so having them under control would mean that a country will have a very big influence on the trade going through them.

Lot of battles throughout the history have taken place because of the straits, with the main reason being that they were bringing lot of control, wealth, and political power.

When a country controls a strait, or more straits, all the trade that goes through it has to be with a permission of that country. In order to make lot of profit, the government of the country imposes taxes, and by pretty much doing nothing, the country manages to get enormous amount of money by just possessing the strait/s.