Build your own fictional nation, expand, and conquer.
In 1921 after years of fighting the poisonous gasses used by most of the fighting nations took its toll, and certain chemical compounds caused crops to fail, and livestock to die out. Seeing no true victory on the horizon these nations despite still enemies remain at another uneasy truce, but it cannot last. Modern weapons are starting to appear now, and jet technology can make travel even faster.
After 25 years of patience war has come.