The Green Line is an 1944 animated short. It is the 13rd short of the Mighty Mouse theatrical series.
In the town of Nowhere, the main street is divided by a broad green line. The mice live on one side. The cats live on the other, and never cross over the line, until an evil spirit convinces one of the cats to cross the line. Chaos ensues until Mighty Mouse arrives to defeat the evil spirit cat in a battle in the sky. The evil spirit cat crashes to the ground and burns up in a flaming pile!