December 18th is the United Nations International Migrants Day.
According to the United Nations:
The total number of international migrants has increased from an
estimated 175 million in 2000 to 244 million persons in 2015. Nearly two
thirds of all international migrants live in Europe (76 million) or
Asia (75 million). Migration is now more widely distributed across more
countries. Today the top 10 countries of destination receive a smaller
share of all migrants than in 2000.
One of every ten migrants is under the age of 15. The
impact of remittance flows is also significant having reached $436
billion in 2014 – far exceeding official development assistance and,
excluding China, foreign direct investment.
Mounting evidence indicates that international migration is usually
positive both for countries of origin and of destination. Its potential
benefits are larger than the potential gains from freer international
trade, particularly for developing countries.
The JCU Library has lots of resources on human migration and Australia if you'd like to learn more.