The League of Nations failed for many reasons. One of them being the fact that the United States didn't join. The American people didn't support the League this caused them not to join. The United States if very important in establishing a global power. You would also need China and Russia to join. They did but it doesn't work without all three,
A) Hijrah is the even that marked the beginning of the Islamic era. Hijrah is the journey of the Islamic prophet Muhammad and his followers from Mecca to Medina in 622 AD.
A Greek Polis is a city state
