When the government of Charles IV went to war with revolutionary France in March 1793, it launched Spain into a cycle of conflict that was to last, with only brief interruptions, for the next two decades. Almost from the first, Spain proved unable to hold its own among the great European powers. Following the execution of Louis XVI in 1793 and the rupture of the Family Compact, Spain's long-standing alliance with France was abandoned and, to combat the rising revolutionary power north of the Pyrenees, Charles IV joined with Britain, Spain's traditional enemy, to fight its traditional ally. This was an unhappy and unsuccessful alliance. After some early successes against France in 1793, the tide of war quickly turned against Spain and, after suffering heavy losses, Madrid was forced to renew the Franco—Spanish alliance in order to resist the rising power of Britain, the old enemy. This led to an immediate renewal of conflict between Spain and Britain. In August 1796, the Treaty of San Ildefonso joined Spain and France in an offensive and defensive alliance against Britain; in October 1796, Spain declared war on Britain. The decision was to prove a disaster for the Bourbon monarchy. Britain now turned the full might of its seapower against Spain, defeating the Spanish navy at Cape St. Vincent in 1787, thereby depriving Spain of commerce and revenue by cutting essential trade routes between Spain and its American colonies, and, in 1798, seizing Trinidad for use as a platform for attacks on Spain's South American territories.