The French Renaissance saw a spectacular cultural development and the first standardisation of the French language, which would become the official language of France and the language of Europe's aristocracy. It also saw a long set of wars, known as the Italian Wars, between France and the House of Habsburg. French explorers, such as Jacques Cartier or Samuel de Champlain, claimed lands in the Americas for France, paving the way for the expansion of the First French colonial empire. The rise of Protestantism in Europe led France to a civil war known as the French Wars of Religion, where, in the most notorious incident, thousands of Huguenots were murdered in the St. Bartholomew's Day massacre of 1572. The Wars of Religion were ended by Henry IV's Edict of Nantes, which granted some freedom of religion to the Huguenots. Spanish troops, the terror of Western Europe, assisted the Catholic side during the Wars of Religion in 1589–1594, and invaded northern France in 1597; after some skirmishing in the 1620s and 1630s, Spain and France returned to all-out war between 1635 and 1659. The war cost France 300,000 casualties.