Why is the National Day of Bahrain celebrated on 16 December ?

Answer 1

1. Bahrain's National Day is on 16 December, but the country had two independence dates:
(a) 15 August 1971 is the date of independence from the UK;
(b) 16 December 1971 is the date of independence from British protection.
http://lexicorient.com/e.o/bahrain.htm
http://www.theodora.com/wfbcurrent/bahrain/bahrain_government.html

2. In 1861 Britain signed a treaty of protection with the Al Khalifa.
(a) The Al Khalifa were a clan of the Bani Utub tribe who had invaded and captured Bahrain in 1783. Sixteen years later, the Al Khalifa had been evicted from Bahrain by the Sultan of Oman, only to regain control of the country in 1811. So the clan's occupation of the territory had been for less than one hundred years, and had been challenged by neighbours.
(b) Under the 1861 treaty, known as the Perpetual Truce of Peace and Friendship (and revised in 1892 and 1951), Britain promised to protect Bahrain from all aggression by sea and to lend support in case of land attack. Furthermore the British promised to support the rule of the Al Khalifa in Bahrain, securing its unstable position as rulers of the country. However, the treaty specified that the ruler could not dispose of any of his territory except to the United Kingdom and could not enter into relationships with any foreign government without British consent. This latter stipulation would be a severe limitation upon any independent nation. The treaty, and British protection came to an end on 16 December 1971.
http://en.wikipedia.org/wiki/History_of_Bahrain