Complex sentence: During World War 1 American forces encounter an unknown device, along with an unknown mineral called Siberite, decades later they find out that the mineral is a catalyst for cold fusion, they find that it is the fuel for the device named EON.
Split into simpler sentences: During World War I American forces encounter an unknown device, along with an unknown mineral called Siberite. Decades later they find out that the mineral is a catalyst for cold fusion, and it is the fuel for the device named EON.