Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an atomic weight of 1.00794 u, hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its plasma state. Naturally occurring elemental hydrogen is relatively rare on Earth.

Hydrogen in Southern Victory
Shortly after the end of the Second Great War, captured Confederate physicist Henderson V. FitzBelmont shared the theoretical possibily of a hydrogen-based superbomb with U.S. General Abner Dowling. The idea horrified Dowling, but the U.S. government quickly began building one.

Hydrogen in Worldwar
The Race had made use of hydrogen as a fuel for their vehicles for milenia before they invaded Earth in 1942. The Race was initially perplexed by humanity's decision to use petroleum for transportation, as they saw it as an utter waste of the resource.

After the Peace of Cairo, most of the oil-rich regions of the world were under Race control. The free not-empires of the world soon adopted hydrogen as a fuel.

Hydrogen in The Two Georges
For much of the history of airship travel, hydrogen was used as a fuel. However, it was eventually subplanted by the non-flamable coronium.