The Undying Mercenary on the Otherworldly Front Line

In 2X32, the parallel-world Empire of Moloxia launched an invasion of the Northern Federation on the other side of the World Island. But by then, the Northern Federation had already mastered mature composite armor technology, and the war gradually bogged down after the initial advantage...

A post-apocalyptic war story with a mix of technologies. An alternate world where one-third of the technology resembles that of the modern world.