Not much has been uncovered about the origin of this war. From the little pieces of evidence we have gathered, we can assume it began circa 1400. In these days, Tractors and Lawnmowers had very little technology. This resulted in early battles being crashes, and explosions. Tractors obviously weighed more and had the upper hand.
Early battles consisted of crashes and explosions. Tractors out-classed lawnmowers in every category aside from speed. The most important of the earlier battles, is the Great Plain Standoff. After this way, the Tractors were horribly distraught. This is when the lawnmowers took the upper hand in the war. Around this time we can estimate that the Falloon population dropped about 45,000. This estimation is possible because of fossil evidence, and a great rise in Ice Reed population.
Great Plain Standoff
The Great Plain Standoff was a battle towards the beginning of the Tractor-Lawnmower War. Tractors and Lawnmowers lined up, and faced each other. They both charged in at the same time. It seemed that the Tractors had a nearly 100% win. Another line of lawnmowers came from behind and ambushed them. This took the lives of 3,458 Tractors. Only 18 Tractors managed to survive.
The main war is still going on to this day. Many technological advancements were made to help Tractors with their stealth, power, and speed. The Lawnmower population has been dwindling (about 78% less than the beginning of the war). This leaves only ~ 264,000 lawnmowers left to fight the war. Many lawnmowers have gone into hiding. About 50,000 are left to fight the war. About 20,000 come out of hiding each year.
Fun Fact: Lawnmowers actually used to reside in the Dumbass Realm, but have since been banished to Earth.