The Kachin organization has been taking a political stand. They used an old document called the Panglong agreement, which is the document that formed Burma. With that, Burma gained independence from the British. With the agreement, it meant that with all ethnic leaders at that time, Burma would have a kind of federalist country, but that dream never happened.
Even though Kachin armed groups had a ceasefire, as you mentioned, for 17 years, clashes broke out last year. Those clashes happened in a very strategic area. It's called the Irrawaddy River. Around the river, there is a mega-dam project being built by Chinese companies, blocking the two rivers. In that area, Kachin fighters are also quite active, and they want to keep the authorities under control. On the other hand, the Burmese army is trying to push them back. That is how they started the fighting last year.