The simple way to measure this is to find out the GDP the population and the debt. Those metrics will answer your question, or at least give you the beginning of an answer.
Country population GDP Debt.
Sudan 40.78 45.82 60
Cuba 11.78 87.13 25
North Korea 25 12 10
Japan 126 4872 11050
Population is in millions
GDP is in billions
Debt is in billions
Quick answer: Cuba is likely in the best shape,
Perhaps North Korea is next
Sudan is third and very high in debt.
Japan is going to have its problems.
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Now this is a very hard question to answer. First of all you need to understand GDP. That stands for Gross Domestic Product. It means the amount of money a population engages in. It is measured in Billions of dollars.
If you buy a package of chewing gum, that becomes part of the GDP. If you buy a car or a house or have your income tax filled out or you pay school fees that's part of the GDP, If you export oil or send your aunt Rachel a shawl and she lives in Ireland, that's still part of the GDP. In general, the higher the GDP the richer the country.
But
Lurking in the background is the debt. You may be OK now with a high GDP, but if you have a high debt to GDP ratio, woe unto you for sooner or later you will have to pay it and that will break your economy. Japan no longer looks so rosy. They owe roughly three times what the produce in one year.
Put another way every man woman and child in Japan owes 87698
Do not think you are safe if you live in the United States.
Every man woman and child in the US would have to pay 60000 to clear the US federal debt. Can your family do it? Mine cannot.
It looks to me of the four countries listed, Cuba is the best one economically. The GDP is about 7400 dollars ( every man woman and child produces about 7400 dollars per year while their debt is 2222 per person. Still high but nowhere near 60000.