Although i knew in advance that Argentina was a rich country beforehand, i recently heard that Argentina around the early 20th centuary (around 1900-1950) was one of the richest countries in the world. The country was even richer than, apparently, a lot of european nations. But today, Argentina is still not a fully developped country and it's history there has been military junta, and several bad financial crisises, than has hurt the country's economy pretty bad. But how was it that Argentina became such a poor country with a rocky economy when it, no less than 100 years ago, was one of the richest countries in the world??
Can I just point out that Argentina is nowhere near being one of the poorest countries in the world. It has a higher GDP per capita than some EU member states, and is ranked as having very high human development by the UNDP's Human Development Report.
This is not to say that it isn't relatively less well off than it was at the beginning of the 20th century.
Argentina's economy was peaking in 1914, IIRC. Argentina was just another victim of the First World War. Following the Napoleonic Wars, and the Spanish American independence movements, there was a new European nation looking to gain a foothold. The United Kingdom. South America was particularly important to the UK, and formed part of the "informal empire" (the British did not take any part in the administration, but bound economies to theirs). The First World War devastated the British economy, and the more open trading economy that opened up afterwards meant there was far little bi-lateral trade between the two.
Now this wasn't all doom and gloom, Argentina lost some economic power, but was still a fairly important regional power. However, the Second World War revealed the true weakness in the current world order, and the United States was left to pick up a large share of the pieces after it. However, Argentina had stayed neutral in the war, leading to less cordial relations than with most places in the world. Argentina became a nation more geared toward pursuing self sustainability over free trade like the rest of the world.
The cheap labour that had made Argentina rich because of exporting to the British Empire were no longer needed, the population remained uneducated, there were several coups over the latter half of the century. It basically didn't become worth investing in the Argentine economy. In the pre-war era Argentina may have had a large economy, but the majority of that came from foreign investment. It was a situation much like that of Weimar Germany (Argentina also had high inflation rates).
The country just isn't ready yet to be a regional power yet. However, that could change in a generation, but it might not. Look at India, at the turn of the 20th Century it was the third largest economy in the world (eclipsed by the US and UK), with 70 years of democracy, they still are batting far below what a nation of its manpower could be.
There is a detailed answer from a few months ago.
The TL;DR from the same post:
"Argentina became a leading agricultural exporter by 1910, held a prominent role in global trade and attracted significant foreign capital investment to finance railroads and export industries. In the 1920s agricultural prices collapse and global trade grinds to a halt following the recession, hitting Argentina's agricultural export heavy economy doubly hard and sending it into a tailspin. The debt Argentina had taken on to finance its growing export industries is now unserviceable due to trade and price declines, leading Argentina to default on its loans, cause its currency to collapse, and making it difficult to raise capital for future industrialization. The slowdown in the immediate aftermath threw Argentina out of the top 10, and the difficulty of accessing capital kept them from industrializing and realizing the growth rates of competitors in the decades thereafter."