Throughout the period, agriculture and infrastructure continued to expand, benefiting from massive British investment. The first railway , built in 1854, connected Buenos Aires to the farms and estancias in its vicinity. By 1880, the railway network carried over three million passengers and over one million tonnes of cargo, and between 1857 and 1890, nearly 10,000km of track were built. Wool production became such a strong sector of the economy in the second half of the nineteenth century that exports dwarfed those of hides, and sheep outnumbered people by thirty to one. Sheep farms were small, privately owned or rented family concerns, in contrast to the huge impersonal estancias. This saw the growth of a strong middle-class group in the provinces. Also transforming the countryside was the boom in export crops such as wheat, oats and linseed. Another development of major importance was the invention of refrigerator ships in 1876, enabling Argentina to start exporting enormous quantities of meat to the urban centres of newly industrialized Britain and Europe. The creation of farm colonies with European immigrants was part of a general policy of encouraging white immigration to the country. Significant numbers of French people arrived in the 1850s, followed later by groups of Italians, Swiss and Germans. As a consequence of this, Santa Fé saw a tenfold rise in population between 1858 and 1895. In Buenos Aires and other areas, the age of latifundismo had begun as huge tracts of land were bought up by Argentine speculators hoping to profit by their sale to railroad companies. In the meantime, they were rented out to sheep farmers and sharecroppers. Between 1880 and World War I, an astounding six million immigrants came to Argentina. Half of these were Italians, a quarter Spaniards while other groups included French, Portuguese, Russians, Ottomans, Irish and Welsh. In 1895, foreigners represented nearly one-third of the population of the Buenos Aires city, which grew in size from 90,000 in 1869 to 670,000 in 1895. Many came in search of land but settled for work either as sharecroppers in estancias and latifundios or as shepherds, labourers and artisans. This convulsive influx caused occasional resentment among Argentines, particularly during periods of economic depression, which were usually sparked by events abroad. Growth depended largely on foreign investment and the country was susceptible to economic slumps like the one that affected Britain in the 1870s, prompting occasional debate about protectionism . Immigrant participation in the political life of the country was certainly not encouraged, and few took up Argentine citizenship on arrival, because citizens were obliged to perform military service. Generally, though, immigrants were welcomed as part of the drive towards economic expansion and colonization of the countryside.