The establishment of the bilateral framework was the most significant regulatory legacy of the Chicago Convention. The Chicago Convention established a number of guiding legal principles known as 'freedoms'. Additional freedoms were added later to comprise what would become known as the seven freedoms of the air. Modern air law is based upon the legal principles for maritime navigation long established in international conventions. The 1982 United Nations Convention on the Law of the Sea (UNCLOS) represents the current legal regime for international maritime navigation. Combined with other developments the initiation of polar routes, the opening of Chinese, Russian, and Mongolian airspace; the introduction of longer range aircraft, growing airline alliances, and the opening of new Asian hub airports Tokyo's capacity constraints have induced North American carriers to bypass Narita altogether and either fly directly to Asian destinations or connect through other hubs such as Incheon, Beijing, or Shanghai.