Spain remained officially neutral in both wars.

At the time WWI broke out Spain was one of the least developed countries in western Europe, still recovering from losing pretty much all their overseas territories at the end of the XIX century. Spain’s military power was negligible and thus not a desired allied anyway by any of the two sides.

When WWII broke out Spain was a devastated country after a bloody 3 year civil war. Franco had just won this war and was naturally friend of Mussolini and Hitler (both helped Franco win the war) but he firmly kept Spain officially out of the war. It is not really known whether the reason is that Hitler did not agree to the conditions Franco had to support the axis. Despite of Spain remaining neutral, significant numbers of Spanish soldiers fought in both sides. The “division azul” fought alongside the German army - and a Spanish battalion formed mainly by exiled republican and anarchist Spanish was the first one to enter the city during the liberation of Paris.