Actually, the increase in the power of monarchs was a major role in the decline of the Popes. As secular governments became more effective and better organized, they gradually took authority in areas that had previously dominated by the Church. This has continued into modern times, as secular governments largely in the past century in most developed nations have taken control of most health care, education, and higher education, all areas that were largely church functions at the height of the papacy.
Also, the rise of secular governments caused financial conflicts with the papacy. The secular governments needed tax income and wanted to tax lands, or at least to have land used to produce crops which could be taxed. The church controlled vast amounts of land, never paid taxes on it, and generally left much of it unused. Along with the famous conflict over his marriage, the opportunity to seize this land and distribute it among his favorites was a major reason for Henry VIII breaking with the church.