After guaranteeing the independence of Poland, both declared war on Germany on the same day, 3 September 1939, after the Germans ignored an ultimatum to withdraw from the country. When Germany began its attack on France in 1940, British troops and French troops again fought side by side. Eventually, after the Germans came through the Ardennes, it became more possible that France would not be able to fend off the German attack. The final bond between the two nations was so strong that members of the British cabinet had proposed a temporary union of the two countries for the sake of morale: the plan was drawn up by Jean Monnet, who later created the Common Market. The idea was not popular with a majority on either side, and the French government felt that, in the circumstances, the plan for union would reduce France to the level of a British Dominion. When London ordered the withdrawal of the British Expeditionary Force from France without telling French and Belgian forces and then refused to provide France with further reinforcements of aircraft the proposal was definitively turned down. Later The Free French resistance, led by Charles de Gaulle, were formed in London, after de Gaulle gave his famous 'Appeal of 18 June', broadcast by the BBC. De Gaulle declared himself to be the head of the one and only true government of France, and gathered the Free French Forces around him.