Yusuf Ibn Tashfin
Between the years 1009 and 1013 the Caliphate had been swelled under civil war and absolutely ruined the country and this gave the ultimate advantage to the Christian hordes of the North. Under serious threat from the North the Sultans of the different petty states asked for the help of the ruler of Morocco Yusuf Ibn Tashfin "the Saladin of the west" in the defence of "Al-Andulus. He crossed into Spain with a large force and delivered a heavy blow to the Kingdom of Castile, however he could not enjoy is fruits and had to return with the news of the death of his heir.
Correction and reformation
The Emirs and Sultans of the petty principalities had been fighting for so long, they had breached Islamic principalities and racism between Berbers and white Arabs had increased. With all these problems and defaults the great Emir Yusuf Ibn Tashfin realized he had to return and restore the glory of "Allah" in Al-Andulus and so he crossed over once again. Upon restoring order and taking command of Spain he decided he would lead the "Jihad" against the Christians and began a siege of Valencia and drive them out of Spain once and for all.
Siege of Valencia
The first few sieges failed then Yusuf decided to go personally and lead his army. The Valencians were using archers to defend their tower, Yusuf managed to neutralise them by catapulting men into the city, which proved very successful. Despite Valencia being heavily defended Yusuf made another striking blow by capturing the city and leaving Castile on darkness.
Conquest of Castile
Yusuf realised the greatest threat to Muslim Spain was the Kingdom of Castile so he wanted to eliminate this threat, he lead a force of 15,000 men to the North. He besieged Toledo and after a 20 day long battle the city fell and the population was spared. The march continued and city after city was captured, with Yusuf's force being far greater then Alfonso's. Alfonso lead a desperate last stand with a force of 20,000 against Yusuf's 18,000. However, Yusuf was once again victorious crushing Alfonso's army and also killing Alfonso. Remaining forces loyal to Alfonso were besieged at Burgos which ended after only three days. Castile was conquered and a greater part of Spain had been returned to the Muslims.
The conquest of Castile alerted the other Christian Kingdoms and soon they sought an alliance with each other. The various Kingdoms of the Christian north began to set up an alliance to stop Yusuf and even try to drive the "Moors" out of Spain once and for all. The alliance started on the offensive. However, this proved useless. Yusuf's defence tactics were exceptional and strong fortifications stopped the Christians decisively. Yusuf then decided to mount an offensive striking at each Kingdom. Portugal was the first to fall with the conquest of Lisbon and then within a period of two years, he had become master of the North. Each King gave him their sword and accepted Islam.
Offensive against France
With the North pacified and finally brought under Muslim rule, the Moors could now focus their attention towards Southern France, which had not been invaded nor raided for some time. A strong force 30,000 men was gathered and sent, crossing the French border and seizing towns and villages.