Ethnic conflict. Which isn't exactly communal in nature.
The two parties are Meitei who are Hindu and Kuki who are Christians.
It has more to do with land rights and political representation. Meiteis are more integrated with mainstream society and they dominate the government sector and political spectrum. Kukis are hill based tribes and aren't as well represented.
The conflict started due to Meitei demanding (Scheduled Tribes status) the Kuki who already come under ST classification saw this as a threat to their rights, as currently Meitei could not buy land in hill areas but after getting this status they could also Kuki's reservation rights would be affected.
The area borders Myanmar and for decades there was FMR (Free movement regime) where people on both sides could openly cross to other side. This has been restricted now. So the contention by Meiteis was that many illegal Myanmarese had joined the kukis.
Both these groups have armed groups. Decades back some groups asked for secession from India, but after talks and supression by army in some cases the more hardcore groups were eradicated and others signed peace treaties with India and either disbanded or stopped their activities.
So yeah this is the essential gist of it. Currently there are occasional flare ups but the Indian army is posted there for controlling this.