"slash and burn" method is a widely used method/practice of growing food and crops (agriculture) This means to burn an area of land with forests and trees making sure any and all vegetation is burned. The ash left makes a cleared land filled with a nutritious and rich layer of land which help to fertilize your crops
I mean... Eventually some kings left the Papal authority. However, remember the crusades? It united nearly everyone in Europe. Some to the point of making new states.
