As the twentieth century wore on, so the pressure for political change increased. Power still remained in the hands of a tiny minority of the landed and urban elite, leaving the professional and working classes of the rapidly expanding cities unrepresented. From 1890, a new party, the Radical Civic Union (Unión Cívica Radical or UCR), agitated for reform but was excluded from power. A sea change came with the introduction of universal manhood suffrage and secret balloting by the reformist conservative president, Roque Sáenz Peña, in 1912. This saw the victory of the first radical president, Hipólito Yrigoyen , in 1916, and ushered in thirteen unbroken years of radicalism, under him and his associate, Marcelo T. de Alvear. Soon after World War I, growth picked up again, with the expansion of manufacturing industry, but the benefits of economic growth were far from equally distributed. Serious confrontations between police and urban strikers in Buenos Aires led to numerous deaths in the Semana Trágica - or Tragic Week - of 1919. This was followed by the 1920-21 rural workers' strikes in southern Patagonia. Most strikers were immigrant peon farmhands from the impoverished Chilean island of Chiloe but there was also a handful of labour activists, Bolsheviks and anarchists. A first strike had taken place in 1920, sparked by the fact that peons had been unable to cash in or exchange the tokens with which they were paid by wealthy sheep barons - many of them British. The protest expanded to include a raft of other grievances concerning working rights and conditions, and radical factions latched onto what was, at root, a fairly conservative phenomenon. Shaken and surprised, the estancia owners promised to arrange payment, but when this was not forthcoming, a second strike was unleashed, this time releasing far more in the way of pent-up anger and frustration. Incidents of Luddite vandalism, rape and acts of violent lawlessness were used by opponents of the strike to panic the authorities, now better prepared, into brutal repression . The final tragedy came with the massacre in cold blood of 121 men by an army batallion, at Estancia La Anita. Later, the radicals introduced social security and pro-labour reforms.

By the end of the 1920s, Argentina was the seventh richest nation in the world, and confidence was sky high. Britain remained the country's major investor and market - as revealed in a confidential report by Sir Malcolm Robertson, Ambassador to Argentina, in 1929: "Argentina must be regarded as an essential part of the British Empire. We cannot get on without her, nor she without us." This was a nation that people predicted would challenge the United States in economic power. Within fifty years, however, Argentina had fallen to the status of a Third World power, and the loss of this golden dream of prosperity has haunted and perplexed the Argentine conscience ever since. This decline in status was not constant, but the world depression that followed the Wall Street Crash of 1929 marked one of the first serious blows. The effects of the crash and the collapse of export markets left the radical regime reeling and precipitated a military takeover in 1930 - an inauspicious omen of what was to come later in the century. The military restored power to the old, oligarchic elite, who ruled through a succession of coalition governments that gained a reputation for fraud and electoral corruption. Economic changes continued to shift away from the agrarian sector during this period, and by the late 1930s, the value of the manufacturing industry overtook that of agriculture for the first time. Immigration continued apace, with one important group being Jews, fleeing persecution in Germany.