I’m not sure but i believe it is b) higher birth rates and death rates
Answer: Economic migrants are drawn towards international migration because of the prospect of higher wages, better employment opportunities and, often, a desire to escape the domestic social and political situation of their home country.
All of the countries were having a battle of who could build the biggest bombs, guns, tanks, weapons, technology, etc. which created tension between rival countries. everyone was afraid of the next country being too powerful. Hope it makes sense :-)
