I presume you mean LEDCs (Less Economically Developed Countries). The answer is all countries in the Southern Hemisphere save from New Zealand and Australia. Sounds crazy but it's true.
There are poor people in all parts of the world.
Poor countries
In some parts of the world, slavery would still exist.
Plague exists in many parts of the world and in Texas USA.
All over the world
percentage of the wealthy and poor in the world
yes , most parts of Vietnam are poor.
Some parts of Africa are poor, some are not.
Yes famine still exist in many parts of the world.
China centuries ago. Today they are grown in CA and other parts of the world.
The Abacus.
there are still people today that own slaves in some parts of the world