The early days of the Third Republic were dominated by political disruptions caused by the Franco-Prussian War of 1870–71, which the Republic continued to wage after the fall of Emperor Napoleon III in 1870. Harsh reparations exacted by the Prussians after the war resulted in the loss of the French regions of Alsace (keeping the Belfort district) and Lorraine (the northeastern part, i.e. present-day département de la Moselle), social upheaval, and the establishment of the Paris Commune. The early governments of the Third Republic considered re-establishing the monarchy, but confusion as to the nature of that monarchy and who should be awarded the throne caused those talks to stall. Thus, the Third Republic, which was originally intended as a provisional government, instead became the permanent government of France.
The French Constitutional Laws of 1875 defined the composition of the Third Republic. It consisted of a Chamber of Deputies and a Senate to form the legislative branch of government and a president to serve as head of state. Issues over the re-establishment of the monarchy dominated the tenures of the first two presidents, Adolphe Thiers and Patrice de MacMahon, but the growing support for the republican form of government in the French population and a series of republican presidents during the 1880s quashed all plans for a monarchical restoration.
The Third Republic established many French colonial possessions, including French Indochina, French Madagascar, French Polynesia, and large territories in West Africa during the Scramble for Africa, all of them acquired during the last two decades of the 19th century. The early years of the 20th century were dominated by the Democratic Republican Alliance, which was originally conceived as a centre-left political alliance, but over time became the main centre-right party. The period from the start of World War I to the late 1930s featured sharply polarized politics, between the Democratic Republican Alliance and the more Radical socialists. The government fell during the early years of World War II as the Germans occupied France and was replaced by the rival governments of Charles de Gaulle's Free France (La France libre) and Philippe Pétain's Vichy France (L'État français).
Adolphe Thiers called republicanism in the 1870s "the form of government that divides France least"; however, politics under the Third Republic were sharply polarized. On the left stood Reformist France, heir to the French Revolution. On the right stood conservative France, rooted in the peasantry, the Roman Catholic Church and the army. In spite of France's sharply divided electorate and persistent attempts to overthrow it, the Third Republic endured for seventy years, which as of 2018 makes it the longest lasting system of government in France since the collapse of the Ancien Régime in 1789.
The Franco-Prussian War of 1870–1871 resulted in the defeat of France and the overthrow of Emperor Napoleon III and his Second French Empire. After Napoleon's capture by the Prussians at the Battle of Sedan (1 September 1870), Parisian deputies led by Léon Gambetta established the Government of National Defence as a provisional government on 4 September 1870. The deputies then selected General Louis-Jules Trochu to serve as its president. This first government of the Third Republic ruled during the Siege of Paris (19 September 1870 – 28 January 1871). As Paris was cut off from the rest of unoccupied France, the Minister of War, Léon Gambetta, who succeeded in leaving Paris in a hot air balloon, established the headquarters of the provisional republican government in the city of Tours on the Loire river.