What is the Great Divide?

The Great Divide is one of the longest running wars in the Alternate Century Era. (or A.C.E. as it is known in the Kuro Series) The War; which was between many small organizations and groups; lasted over 100 years with many innovations in technology being made. The most prominent of these achievements is a giant robot simply referred as a "Mecha" . The Mechs became the biggest advantage in this long winded battle, towards the end of the conflict almost all major factions had an entire army of Mechs at their use. However the war was put to an utter halt when a single robot appeared before them...