In the 1880s, when electricity had passed the experimental stage, the economy entered a period of severe depression that left investment, rural migrations and urban concentration at unsatisfactory levels; by 1901, only one fifth of the French population lived in towns of more than 20,000 inhabitants. In the electrical machinery sector, successful firms were those that had access to foreign patents and capital and specialized in transport. Among them one finds Thomson-Houston, established in 1893 to build street-cars and trolleys; after ten years of experience, the firm had supplied 60% of the French urban transportation network, with strongholds in Bordeaux and Paris. By a series of legislative acts, the French state had assumed from 1906, and more decisively after 1919–1925, complete control over the development of the transport system, and over the procedures preparatory to building new power generators.