After the capture of Antioch (June 1098) and the destruction of Ma'arrat al-Numan (January 13, 1099), the Syrian emirs were terrified of the advancing crusaders and quickly handed over their cities to the Franks. On January 14, Sultan ibn Munqidh, emir of Shaizar, dispatched an embassy to Raymond IV of Toulouse, one of the leaders of the crusade, to offer provisions and food for men and horses, as well as guides to Jerusalem. In February, the emir of Homs, Janah ad-Dawla, who had fought bravely at the siege of Antioch, offered horses to Raymond. The qadi of Tripoli, Jalal al-Mulk, from the Banu Ammar, sent rich gifts and invited the Franks to send an embassy to his city.
Fakhr al-Mulk then attacked Mons Peregrinus in September, 1104, killing many of the Franks and burning down one wing of the fortress. Raymond himself was badly wounded, and died five months later in February, 1105. He was replaced as leader by his nephew William-Jordan, count of Cerdanya. On his deathbed, Raymond had reached an agreement with the qadi: if he would stop attacking the fortress, the crusaders would stop impeding Tripolitanian trade and merchandise.
In 1108, it became more and more difficult to bring food to the besieged by land. Many citizens sought to flee to Homs, Tyre, and Damascus. The nobles of the city, who had betrayed the city to the Franks by showing them how it was being resupplied with food, were executed in the crusader camp. Fakhr al-Mulk, left to wait for help from the Seljuk sultan Mehmed I, went to Baghdad at the end of March with five hundred troops and many gifts. He passed through Damascus, now governed by Toghtegin after the death of Duqaq, and was welcomed with open arms. In Baghdad, the sultan received him with great spectacle, but had no time for Tripoli while there was a succession dispute in Mosul. Fakhr al-Mulk returned to Damascus in August, where he learned Tripoli had been handed over to al-Afdal Shahanshah, vizier of Egypt, by the nobles, who were tired of waiting for him to return.
A compromise decided in the course of a dispute beneath the walls of the city, and arbitrated by Baldwin of Jerusalem, allowed the city to be captured: the County of Tripoli would be divided between the two claimants, William-Jordan, as a vassal of the Principality of Antioch, and Bertrand, as a vassal of Jerusalem.

The city fell on July 12, and was sacked by the crusaders. One hundred thousand volumes of the Dar-em-Ilm library were deemed "impious" and burned. The Egyptian fleet arrived eight hours too late. Most of the inhabitants were enslaved, the others were deprived of their possessions and expelled. Bertrand, Raymond IV's illegitimate son, had William-Jordan assassinated in 1110 and claimed two-thirds of the city for himself, with the other third falling to the Genoans. Thus Tripoli became a crusader state; the rest of the Mediterranean coast had already fallen to the crusaders or would pass to them within the next few years, with the capture of Sidon in 1111 and Tyre in 1124