Two hundred years ago, 4 out of every 10 children everywhere died before reaching the age of 5. These numbers were likely collected mainly from advanced countries, but it would not be improbable that the death rate was even higher in nations with endemic tropical diseases. At present, it is only 2.2 out of 1000 in Luxembourg. Other rich countries, and many others are in the single digits (US, 7.1/1000).
Survival has improved everywhere, but there are huge contrasts: Japan is at 3, China 14, and the fifty percent richer Botswana at 53. India is at 56, Pakistan 86, and Sierra Leone trails everyone with 182. Unsurprisingly, there is a very strong correlation with per capita GDP, but countries like Cuba and Sri Lanka outperform their GDP while the US is a significant underperformer.