Thing To Do Today: rule.

 Every war is about who controls a piece of territory. 

The Battle of Borodino by Louis-François, Baron Lejeune

That's all a war can do.

The word comes from the Old French riule. 

Before that, it's quite interesting.

Thing To Do Today: rule. This word comes from the Latin word rēgule, which means a straight edge. 

And if only rulers were straight, then we wouldn't be in this mess, would we?

The Latin word rēgulāre means to control.