Most of the Emigrants from Mecca had left their wealth (or their poverty) behind. Their clans would have re-absorbed the houses they were occupying, passing them to families that stayed. Some of their possessions were seized by others. I wasn’t able to get a firm sense of just how much wealth the city of Mecca received from the exit of the Muslim families. But in any case, Muhammad and his new government in Medina considered Mecca, and the Quraysh clan in particular, an enemy state that had appropriated their wealth. It may be that the attempt on Muhammad’s life had been taken as a declaration of war. What was Muhammad’s new city going to do about it? Not sit there.
It wasn’t long before some of the Muslims — all ones from Mecca — rode out in a war party to see if they could capture some Meccan caravans. They were city-dwelling merchants, but they were also part of the nomad culture that poetically praised the daring courage of raiders. At first the raiding parties were small, but gradually they grew to as many as 70 men, and Muhammad accompanied one of them. They seized whatever the caravan was carrying, and they captured the men to hold them for ransom, a typical feature of raiding. But in one caravan raid, a Meccan man died, and after that, Mecca’s leaders decided to fight back.
In past revelations at Mecca, Allah had told Muhammad to be patient with the unbelievers. Now, in Medina, the revelations went the other way. The second Surah of the Quran is called al-Baqarah, “The Cow,” because it talks about the golden calf of Exodus. Although it appears early in the Quran, it was actually a later revelation from this period at Medina. The Surah describes Allah as the “enemy of unbelievers.” (2:98) Muslims are directed to fight to the death against anyone who wages war and does not surrender. (2:191) They must retaliate even during sacred months, and they must persist until there is no more persecution. (2:194) Fighting would now be obligatory even if they didn’t like it. (2:216) Context suggests that Mecca was the main target of this new aggressive policy, since other verses talk about making pilgrimage to Mecca.
About two years after the Muslims had left Mecca, they decided to target a very rich caravan led by one of Mecca’s rulers. Almost all of the Emigrants from Mecca joined the war party, and additionally many of the Helpers, the Medinan natives, came too. They numbered about 300 men with 70 camels. However, the Meccans got wind of it, re-routed the caravan, and turned out in force to meet the Muslims. Most of the clans participated, adding up to around 1000 men. As the armies faced each other and waited for a decisive moment to either attack or go home, some of the Quraysh clans went home. But among the remaining Meccan war party were many relatives of the Muslims, including Muhammad’s uncle Abbas and Ali’s older brother.
What to do? The Muslims could have just gone home, since they were not prepared for a real battle. After deliberating, they chose to fight; Muhammad spent a night awake in prayer over the decision. One of the Medinans suggested that they occupy or destroy all of the wells in the Badr Valley, and they did. Arabian battles apparently began with duels between champions; the Meccans sent out three champions who declared they would drink water from a Muslim-held well or die. Muhammad sent out Ali and two others. One of them was seriously wounded, but Ali won his duel. Soon after these duels, there was a charge and general melée.
Even outnumbered, the Muslims still won the battle. In human terms, we know that the group that has more conviction often wins, since an army is only as strong as the discipline of its individual members. The Muslims believed angels fought with them, while the Meccans probably had mixed feelings about what they were doing. Some of the chief enemies of Muhammad were killed in the battle, but at the end, the Muslims also held a number of living captives.
Based on their success in this battle, Muhammad’s team was able to start forming more alliances to isolate and box in Mecca. Mecca’s wealth depended on running caravans between Yemen and Syria, and there were only so many roads the caravans could take. Some Arab tribes that lived along the Red Sea coast allied with Medina, making it unsafe for Meccans to pass through their territory. Mecca countered these moves by forming or reinforcing alliances with tribes near Medina. The region began to polarize, with some allied tribes also adopting Islam.