The major factors affecting bitcoin are :
Change in government - it's simply means when another government enter there's will be reduction or addition of some policies.
Political instability - when political system in the country is not stable, everything will get down.
If this factor occurs then the price of bitcoin will not fall very far and will even rise again very quickly.
This factor has little effect on the decline in bitcoin prices, in my opinion the most influential factor on bitcoin prices are investors who buy bitcoins at very low prices so that sellers cannot sell their bitcoins at high prices.