
The fact that there seems to be a reversal of cause and effect in Gall Force (in that the Solnoids are created hundreds of thousands of years after they rendered themselves extinct) suggests that time travel is involved. control, and the Boomers are mostly used for civilian rather than military purposes.
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The strategic nuclear arsenals which destroy the world in Gall Force Earth Chapter are instead neutralised by orbital laser cannons under U.N. In Bubblegum Crisis, the same basic technologies are discovered a good century earlier with different results. Eventually this leads to the extinction of the human race, except for one ship consisting of female refugees who flee into space to recreate the Solnoid race. These technologies triggered a planet devastating war in the 22nd century because first, the power blocs couldn't decide how to share them, and then the NME cyborgs that were grown from traces of Paranoid flesh to fight in the war rebelled. In Gall Force: Earth Chapter, we learn those technologies weren't invented by humans but just copied from relics discovered on the moon which survived the battle which destroyed Chaos.

The anachronistic technologies in BGC, the Boomers, power armour and the orbital energy cannon are all reflected in Gall Force with the "alien" Paranoids and the weapons used to fight them. Bubblegum Crisis is what happened when the Gall Force timeloop collapsed
