Even before contact with Europeans peoples of northern Asia and of North America hunted polar bears, especially for their fur and blubber. This led to a drastic decline in the population in the 50s and 60s. In 1973, Canada, USA, Denmark, Norway and the Soviet Union, put an agreement in place that would limit the hunt at least. Canada and Greenland 2009, signed an additional agreement, which is to limit the hunting quotas to sustainable levels.
The protective measures resulted in an increasing number of polar bears from about 20,000 to 25,000. On the CITES Conference of 2010, the strict interdiction of commerce outside of the 5 countries with polar bear population has been turned down. More recently, other factors have been added to the threat of polar bears. Global warming in the Arctic regions! The life of the polar bear is threatened because our earth is getting warmer.
Increasing temperatures causes the Arctic ice to melt earlier. The later onset reduces the possibility of hunting of animals. This leaves less and less time in order to build up the fat reserves needed for staying onshore. This also explains why the polar bears need to get closer to cities and humans, as they try to deal with their food deficit.