Moosa ibn Nusayr made a careful study of the Roman colonizers' administrative division of North Africa and laid down the military strategy required to defeat them. This consisted of:
- Choosing loyal and proficient commanders.
- Having direct contact with the soldiers through constant discussion and personal encouragement.
- Gradually clearing off North Africa of the Romans and their protégés, beginning from the Muslims' base at Qayrawaan and steadily moving westward.
By the time Moosa sent armies to Morocco; the inhabitants of the region had already known about Islam and heard of the military strength of the Arabs as well as of their fair treatment of the people under their rule. All of these factors, besides the Roman's inhuman treatment and exploitation of the North Africans, caused many Moroccan tribes to join the fold of Islam and welcome the new conquerors. Thus, with the exception of one or two coastal towns, the whole of North Africa came under Muslim rule through the tremendous and untiring efforts of Moosa .
As a true Muslim who believed in the equality of people, regardless of their language or race, and as a clever administrator, Moosa chose the Berber, Tariq ibn Ziyad to be governor of Tangier and its surroundings. Before leaving Morocco, Moosa left around one thousand seven hundred and fifty fighters and a number of religious scholars to teach Islam to the newly converted Muslim inhabitants of the region, who soon became active members of the community; It is also noteworthy that Tariq ibn Ziyad had a strong army that consisted of twelve thousand men.
By then, only one coastal town was left in the hands of the Roman governor of the area, namely the town of Ceuta (or Cebta as called by the Arabs). Leaving that town in Roman hands under the command of Julian, who was its governor, seemed to have been a very intelligent military and political move on the part of Moosa for through that town the Muslim armies could closely follow the Roman activities in the region and learn about what was going on the other side of the narrow strait (later to be called the Strait of Gibraltar), since the Iberian Peninsula was only a few miles away from Ceuta.
With the defeat of the Romans and having therefore gained total control over North Africa, Mooaa successfully finished the first part of the task. But from past experience, he realised that the Muslim control of the land was not sufficient to keep North Africa safe from Roman attacks and raids. Since his youth he had learnt that the Romans could always use their well-trained and well-equipped naval forces to launch attacks against the coastal areas. So one of the first things he did upon his return to his base at Qayrawan was to expand the ship-building yard earlier established by his predecessor Hasan ibn An-Nu'man in the city of Tunis. The factory (called Dar as-Sin'ah in Arabic) was designed to build warships, and it had craftsmen brought from different ports in the Muslim World, especially Egypt. Other arrangements to ensure easy passage of the ships to and from the Mediterranean Sea were made under instructions from our hero. Thus, the shores of the newly liberated North Africa became safe from Roman attacks.
Peace and stability achieved, many parts of the region began thriving and rapidly developing under Muslim rule. To ensure better security for the coastal area, Moosa occupied some strategic islands in the Mediterranean Sea. The road to Europe was being paved from the East by Maslamah ibn 'Abdul-Malik . In the West, Moosa was already studying the possibility of taking Islam to the Iberian Peninsula, when Julian, the Governor of Ceuta, came to him seeking help against Rodrigos, King of Spain, who had usurped the throne from its legal heirs and mistreated Julian's daughter who was a guest at the Spanish Court in Toledo. Moosa wrote to the Caliph in Damascus asking for permission to invade Spain, but the Caliph was hesitant and ordered him instead to postpone the attack until he had sent scouts and small bands to study the military situation practically. Tareef was chosen commander of about four hundred Muslim commandos who were transported to Spain on board ships provided by Julian himself. The Muslims first set foot on the Island of Palmas (later called Tareef) and then the Iberian Peninsula itself in Ramadan 92 A.H. The raids were successful, and Moosa was convinced of the necessity of conquering Spain. Orders were given to the Berber Muslim commander Tariq ibn Ziyad to launch the invasion of Spain. The crossing was achieved, and the Muslim army was stationed at the mount now called Gibraltar (from the Arabic 'Jabal Tariq' which means 'The Mount of Tariq.')
Moosa himself went to Spain to complete the Muslim conquest of that land, which he successfully did. This was the beginning of a new era for Spain and Europe. For the next eight hundred years Spain was under the Muslim rule that brought civilisation to that peninsula (then known as Al-Andalus), from where the sparks for the Renaissance and the torch of learning were carried to the whole of Europe and the Western World.
When Spain was conquered, Moosa was already in his seventies. It was time for him to retire when the Caliph in Damascus recalled him from Spain back to the east. Caliph Sulayman ibn 'Abdul-Malik later asked Moosa to accompany him to Makkah for pilgrimage.
Back at his birthplace Al-Madeenah, Moosa died at the age of eighty, leaving behind a glorious record of continuous victories for the message of Islam and the Muslims.