The geography and ruling imams of North Yemen kept the country isolated from foreign influence before 1962. The country's relations with Saudi Arabia were defined by the Taif Agreement of 1934, which delineated the northernmost part of the border between the two kingdoms and set the framework for commercial and other intercourse. The Taif Agreement has been renewed periodically in 20-year increments, and its validity was reaffirmed in 1995. Relations with the British colonial authorities in Aden and the south were usually tense.