Answer:
The main theory is that Native Americans reached North America from East Asia, more specifically Siberia, around 14,000 years ago.
The reason why this is the most accepted theory is because it has been proven by genetic studes that Native Americans and East Asians share a great degree of genetic similarity.
According to this theory, at that time, the Bering strait was frozen, and formed a land bridge between Siberia and Alaska. East Asians crossed this bridge, probably following wild game, and entered the American Continent.