Argentina was continuously in some kind of economic crisis for the most of the 20th century.
Even not covering recent period because of the 20 year rule in this sub.
I'm more surprised it's still as well off as it is. How fabulously wealthy was it in the early 1900s that a century of decline still makes it ok?
Perhaps this is not surprising, given how popular discourse about Argentina goes, but there are some deeply mistaken premises to your question. Argentina was not in economic crisis continuously during the 20th century, nor has its economy been in constant decline, at least not in the sense of being literally poorer year on year. Argentina and Argentinians are much richer by 2000 than at the beginning of the century.
What has changed is that, in 1900, Argentina would have been counted (by most metrics) among the wealthier countries of the world, and by 2000, it would have been only modestly above the global median, a middle-income country wracked by financial crisis, having been surpassed by countries that used to be much poorer. But this relative decline is not the same as absolute decline.
You might want to check out this thread, especially the excellent answer by /u/aquatermain.