The Spanish for “war” guerra doesn’t sound like it would actually be the same word. But it is!
The Latin words beginning with the harsh gu- sound generally have the same root and are parallel with the English w- words. Think, William and Guillermo, for example. The gu- and w- sounds do sound alike, if you say both in a thick way.
Guerra and War are another great example of this pattern. The English war comes from the French guerre, which in turn comes from the old German verwirren — meaning “to confuse people.” War is confusing indeed and confusing people is indeed a form of warfare.