Although this was an isolated incident that was committed...
Although this was an isolated incident that was committed without the approval of the Prophet (a.s), the Quraysh saw it as an excuse to prepare for a war. They started crying about reparations (qisas) for the life of Ibn al-Hadrami and went ahead in full swing for the preparations for war. They decided that they would attack al-Madinah as soon as Abū-Sufyan returned from his business trip to Syria.
Abū-Sufyan was to return through al-Madinah, that was the usual halt for caravans back and forth Syria. While the people of Makkah were eagerly awaiting Abū-Sufyan’s return, he sent to them a letter through Zamzam ibn `Amr al-Ghifari that the Muslims were planning to attack his caravan near al-Madinah to plunder his merchandise and that they should reach there post haste with all preparations for a war. The Quraysh were almost ready and did start without any loss of time on getting the letter.
Now Abū-Sufyan avoided the normal route and proceeded on his journey along the coast, reached Jeddah in five days and Makkah in another three days. When the troops of the Quraysh reached near Badr, they got news that Abū-Sufyan’s caravan had reached home safely. Some men of Banū-Zahrah said that the caravan had reached home unmolested and therefore there was no need of fighting and that they should return home from there. But Abū-Jahl refused to return home without fighting.
With the attitude of Abū-Jahl it is clear that the intention of bringing the troops was not to protect the caravan but he wanted to fight a war at any cost. The Banū-Zahrah however returned home and did not participate in the war. The story was going the rounds in al-Madinah that Abū-Sufyan’s caravan was to pass along with lot of merchandize enroot to Makkah from Syria and that the warlike preparations were in full swing at Makkah to attack al-Madinah.
“When Allah informed you that the Infidels of Makkah will confront you in two groups, you wanted to have the smaller group in your share.