Why did France grant independence to Morocco and Tunisia in 1956, but not to Algeria?
France's experience with Algeria was considerably more complicated than were cases with Morocco and Tunisia. More than was the case with the latter two countries, psychologically, Algeria became almost an extension of France. In fact, Algeria was even designated a French administrative region. A large population of French resided in Algeria, as well as large number of immigrants from other Mediterranean countries. The depth of the French commitment to its Algerian colony was existential to many. French expatriots living in Algeria saw themselves as settlers in French territory. Neither Morocco nor Tunisia "enjoyed" such status in French politics and culture. Breaking with those two colonies did not involve the level of psychological anguish that drove France to hold on to Algeria in the face of a growing, and increasingly effective, independence movement.
When the Algerian war of independence began in 1954, French military officers fought tenaciously to hold onto "their" colony. The independence movement, led by the National Liberation Front, presented such an emotional jolt to the French, that it precipated the fall of the government in Paris. The decision by new President (and former general and World War II hero) Charles de Gaulle to eventually relinquish control of Algeria was seen as treasonous by many French army officers, resulting in a revolt by those officers against Paris. Attempts on the life of President de Gaulle by army officers angered at the president's Algerian policy became almost common, although ultimately unsuccessful.
While Morocco and Tunisia were colonized by France, neither held the emotional, and consequently political, importance to the French that Algeria held.