Complex sentence: The first two were those of France and the United Kingdom (and previously, the united crowns of England and Scotland) and the third is the independent crown of Canada, which since Confederation has evolved to become a kingdom in its own right.
Split into simpler sentences: The first two were the crowns of France and the crown of the United Kingdom (and previously, the united crowns of England and Scotland). The third is the independent crown of Canada, which since Confederation has evolved to become a kingdom in its own right.