Nimbus Federation Airship Arsenal

What would the world be like if the airplane had never been invented? What would warfare be like if the only form of aeronautics was the hot air balloon? These are some of my concepts which seek to explore such a world of the alternate past.

The year is 1925 and the great war rages on. British, German, and French soldiers have fought the long fight for control over Europe. Their bloody struggle in the trenches had brutalized the heartlands, destroying much of Europes farms and agriculture. In response to this endless fighting, a new force as entered the arena. Using the latest in aeronautic technology, the Nimbus Federation has risen to power and threatens to turn the tides of war in their favor. The Nimbus Federation controls a massive Air-force, the likes of which the world has never seen. Their floating artillery drifts across the continent, descending from the clouds just long enough to capture unsuspecting cities before moving on to their next target.