Worldwide commercial civil aviation expanded greatly after the First World War. Many European countries founded subsidized national airlines (Sabena, KLM, Deutsche Luft Hansa, Air France and others) for reasons of national prestige, security and commerce. The United Kingdom founded Imperial Airways with the mandate of tying together the far-flung regions of the British Empire, providing air mail and passenger services for overseas British and allied territories. In the United States, the conditions of a large land mass, uniform language and culture, large and growing population, and good flying conditions, favoured rapid growth of private airlines. Many regional airlines grew, and looked to expand traffic to Canada and Latin America. In the United States, Pan American World Airways became unofficially virtually the national flag carrier, being given preferential support by the American government in its negotiations with other governments. Conditions in Canada were different from those in Europe and US. Inter-city operations were not the most important aviation sector in the 1920s. Float aircraft, operating on northern lakes and rivers, had become the basis of much commercial aviation for mining, paper industry, medical, police and mail carriage, so many private carriers formed regional airlines to serve this business. Little investment in fixed air strips was required for floatplane operations. About the only government subsidy available was the contract to carry air mail; however, by the onset of the Great Depression, even these mail contracts were canceled, bringing some airlines to the brink of bankruptcy. While Imperial Airways negotiated with Pan Am on the potentially lucrative and prestigious trans-Atlantic route, Canadian interests were at risk. A trans-Atlantic route that bypassed Canadian territory would greatly impede commercial aviation development in Canada. No national airline existed, and none of the regional airlines was able to negotiate with Imperial Airways for trans-Atlantic routes. One route, feasible with the aircraft of the time, would run from New York to Newfoundland to Ireland to London, bypassing Canadian territory completely. International aviation treaties were negotiated, mostly among European countries, after the end of WW I. The Air Navigation Convention signed by European countries in 1920 was an attempt to provide international rules for air traffic. Canada was only weakly represented at negotiations, but obtained an amendment to one article of the convention that would permit Canada and the US to make their own agreements on cross-boundary air regulations; in the event, the United States Senate never ratified the convention and so the Americans never became a party to it. One side-effect of Canadian participation in international air regulations was the establishment of the International Civil Aviation Organization (ICAO) headquarters at Montreal.