There are 4 main causes for the overpopulation of earth; decline in death rate, increase in birth rate, migration and lack of education.
With our medicine and technology as proficient as it is today there are far less deaths due to disease and injury than there was 200 years ago. Our technology has enabled us to create many vaccines, cures and comforts for those in need, and as a result people are living longer and healthier lives then ever before. This is a great thing, but without controls on our birth rate our planet can't sustain all these people who once would have died.
Additionally, we have had an increase in births; so the death to birth ratio is disproportionate. Religion has helped increase the birth rates with pro life and anti birth control beliefs around the globe. By circulating these beliefs, less people are having abortions and not using birth control which results in a population increase. Up until recently people who lived in poverty had always had a large number of kids because the chance of a child's survival was slim, so having more kids increased their chance of passing their genes on. Now these people are still having a lot of babies but with our technology today the babies are surviving, so these families can't sustain life where they live so they chose to move to locations with more opportunities.
Another leading cause of over population is migration; one of the biggest reasons for someone to migrate is to provide a better life for themselves and their family. This is causing many issues because the financial and tax systems can only handle a certain amount of people. When