This is a really great idea guys. You know those cool sinkhole "Gates of Hell" things? Well what if they really were gates to hell and demons erupt from them and begin conquering Europe as an invasion from the province the sinkhole appears in? And then we could have the angels to fight them by pious leaders being able to give land up to the angels. In the aftermath of the war Europe would have to deal with the new angels and demons nations, with questions about how to treat them, should we demand our land back, marriage and children with the angels and demons, etc.