In Morocco by Edith Wharton — Read

The first thing to do was to create a strong frontier against the dissident tribes of the Blad-es-Siba. To do this it was necessary that the French should hold the natural defenses of the country, the foothills of the Little and of the Great Atlas, and the valley of the Moulouya, which forms the corridor between western Algeria and Morocco. This was nearly accomplished in 1914 when war broke out.

At that moment the home government cabled the Resident-General to send all his available troops to France, abandoning the whole of conquered territory except the coast towns. To do so would have been to give France's richest colonies[A] outright to Germany at a moment when what they could supply -- meat and wheat -- was exactly what the enemy most needed.