Simplify the following text for a Grade 11 native English-speaking person.
Original: Tibet and Mongolia signed a treaty called the Treaty of friendship and alliance between the Government of Mongolia and Tibet on February 2 , 1913 , at Urga ( now Ulaanbaatar ) .
Simplified: A Treaty of friendship and alliance between the Government of Mongolia and Tibet was signed on February 2 , 1913 , at Urga ( now Ulaanbaatar ) .