Napoleon knew that he had no time to wage a defensive campaign; he was under threat from all sides. An Allied army of British, Germans, Dutch-Belgians and Prussians was massed in the Low Countries, Austrian forces were concentrating both in the Black Forest and to the South of France and a huge Russian army marched toward the Central Rhine. The most immediate threat was posed by the multinational force in the Low Countries commanded by Wellington and the Prussian Marshal Blucher. Furthermore, Napoleon considered this area of Europe to be most sympathetic to him and realised that he had a good chance of gaining widespread support there. Hence, he planned to strike into Belgium as quickly as possible, before the Allied armies had a chance to form a cohesive force and hopefully defeat the various constituent parts in detail.