The most serious native insurrection since the time of Abd al Qadir broke out in 1871 in Kabylia and spread through much of Algeria. The revolt was triggered by Crémieux's extension of civil (that is, ) authority to previously self-governing tribal reserves and the abrogation of commitments made by the military government, but it had its basis in more long-standing grievances. Since the Crimean War (1854–56), the demand for grain had pushed the price of Algerian wheat up to European levels. Storage silos were emptied when the world market's impact was felt in Algeria, and Muslim farmers sold their grain reserves — including seed grain — to speculators. But the community-owned silos were the fundamental adaptation of a subsistence economy to an unpredictable climate, and a good year's surplus was stored away against a bad year's dearth. When serious drought struck Algeria and grain crops failed in 1866 and for several years following, Muslim areas faced starvation, and with famine came pestilence. It was estimated that 20% of the Muslim population of Constantine died over a three-year period. In 1871 the civil authorities repudiated guarantees made to tribal chieftains by the previous military government for loans to replenish their seed supply. This act alienated even pro-French Muslim leaders, while it undercut their ability to control their people. It was against this background that the stricken Kabyles rose in revolt, following immediately on the mutiny in January 1871 of a squadron of Muslim spahis in the French Army who had been ordered to embark for France. The withdrawal of a large proportion of the army stationed in Algeria to serve in the Franco-Prussian War had weakened France's control of the territory, while reports of defeats undermined French prestige amongst the indigenous population.