Why did the pope support William's campaign?

Pope Alexander II supported William the Conqueror's campaign to invade England in 1066 primarily because he sought to strengthen the influence of the Church in England and saw William as a means to achieve this. By backing William, the pope aimed to promote the idea of a divinely sanctioned monarchy, which would enhance the Church's power and authority. Additionally, the pope viewed the campaign as an opportunity to reform the English church and align it more closely with continental practices. This support was indicative of the broader relationship between the papacy and European monarchs during this period.