1. He had to deal with the feuding tribes of Medina. As a solution, he drafted the Constitution of Medina. The resulting society is agreed to be Islam at its finest.
2. 630 (This is the year in the legend. No ones the actual date. It was year 8 AH)
3. Saudi Arabia
1) -There was hatred and wars spreading among two tribes there called Aws and Khazraj. He (pbuh) made them stop the wars and formed brotherhood between them
-The Emigrants from Mecca left their homes and money in Mecca escaping from the polytheists, so they had no any source of income. He (pbuh) told the Ansar (the ppl who were living) in Madina, that the Emigrants (muhajreen) are your brothers in Islam, so the Ansar welcomed them with open arms. They shared their homes and their bread with them. On numerous occasions, they deprived their own children of food which they gave to the hungry Muhajireen.
-There were three main Jewish tribes in the Madinah. The prophet (pbuh) made a peace treaty with them first, but when the Islamic nation started getting stronger the Jews betrayed that treaty.
-There are much more struggles that faced building the Islamic nations in the Madinah, like the hypocrites who were working as spies for the polytheists in Mecca.
2) Before the prophet (pbuh) return to Mecca, there was a treaty called the Hudaybiyah Treaty, and this treaty was between the Muslims and Qurish with other tribes. That treaty was very oppressive to the Muslims, and it did not allow them to go to Mecca and do their pilgrimage (Haj), but the prophet Muhammed (pbuh) agreed on it. One of the tribes who were with Qurish betrayed this treaty and killed some of the Muslims. Quraish sent a messenger to renew the treaty, but it was too late and did not work. The prophet (pbuh) ordered the army to get ready for fighting. He (pbuh) entered Mecca with little struggles, but no one got killed either from the Muslims or the people in Mecca. That was in 630AD. The prophet (pbuh) asked:
-"O Quraish, what do you think of the treatment that I should accord you?"
And they replied:"Mercy, O Prophet of Allah. We expect nothing but good from you."
Thereupon Muhammad declared: "I speak to you in the same words as Joseph spoke to his brothers. This day there is no reproof against you; Go your way, for you are free."
- Since then Islam is spreading till nowadays
3) Mecca and Medina are in Saudi Arabia, aka KSA. These days the Haj is going on there, and on Friday it will be a celebration or feast for the Muslims, it is called Eid Aladha.