The death rates exceed the birth rates in the US and most (if not all) the western European Countries. Therefore, the �actual� population is truly decreasing in the US and Europe.
What is causing the large increase of population is immigration. As we all know the majority of immigrants in the US is from Mexico. In Eastern Europe the immigrants are from the Middle East. As a result, the Muslim populations are eventually going to be the majority in these countries. I know this is a big concern for countries like Sweden that initially encouraged the immigration as they were looking for help supporting the decreasing workforce. Only time will tell what impact this has on the world, environment, religion, economy, etc.