Theory:

a) Ecological or Natural Causes of Migration
As the name indicates, causes under this category are caused by natural events like earthquakes, floods, volcanic eruptions, drought etc.
 
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Buildings damaged in Earthquake
 
These events seriously affect residents' lives and force the people to leave their native places and settle in new and safer areas. These migrants look for conditions like the availability of water resources, areas free from hazards, pollution etc., to settle.
b) Economic causes of Migration
The economy is one of the most important causes of human migration from one area to another. Millions of people migrate each year in search of better jobs, better economic opportunities and livelihood. Several economic causes determine the level and direction of Migration.
 
The availability of fertile land for cultivation, employment opportunities, business opportunities, development of technology etc., are some of the economic causes that attract migration. Persistent poverty, poor living conditions, and unemployment force people to move out from their native places to places with better employment opportunities.
 
According to the World Migration Report 2020, released by the International Organization for Migration, as of June 2019, the number of international migrants was estimated to be around \(272\) million globally, \(51 \)million more than in 2010. Nearly 2/3rd were migrants.
International migrants comprised around\( 3.5\) per cent of the global population in \(2019 \)compared to \(2.8\) per cent in \(2000 \)and \(2.3\) per cent in \(1980\).
 
Share of Regions in World population and International Migrants by Origin - 2017
S.No.
Name of the region
Total Population
Percentage of global population
International migrants by origin
Percentage of International migrants
1.Africa1,256,26816.636,26614.1
2.Asia4,504,42859.7105,68441.0
3.Europe742,0749.861,19123.7
4.Latin America and the Caribbean645,5938.637,72014.6
5.North America361,2084.84,4131.7
6.Oceania40,6910.51,8800.7
7.Unknownn/an/a10,5604.1
8.World7,550,262100.0257,715100.0
Source: International migration report, 2017, United Nations