In February 1793, the French National Convention declared war on Britain, the United Provinces and Spain. As the French advanced north into the Austrian Netherlands, Britain feared that the United Provinces would fall into French hands.
The Dutch controlled significant ports, such as Amsterdam and Antwerp, and if they fell into french hands, it would mean that British dominance of the seas would be threatened. So Britain demanded that France relinquish the conquered territories.
Spain was preparing to join the coalition against France. Spain was ruled by the Bourbons who were deeply shocked and appalled by the execution of Louis.
By the end of February 1793, France was at war with Austria, Prussia, Britain, Holland, Spain and Pied-Sardinia. They were collectively referred to as the First Coalition.
France suffered a major defeat at the Battle of Neerwinden. Dumouriez also defected to the Austrians, causing the convention to question the loyalty of even its most renowned commanders.
By August 1793, there were British, Spanish, and Austrian troops on French soil, leading to defeat.