Much of the country's land area has been built up from alluvial deposits brought down by the major rivers. The land is mostly flat except for a range of hills in the south-east. It is mainly characterized by wooded marshs lands and jungles with forests regions in Sylhet, Rangamati, Khagrachari and Bandarban Hill Tracts, Sundarbans, Mymensingh and Tangail. The history of Bangladesh has been one of extremes, of turmoil and peace, prosperity and destitution. It has thrived under the glow of cultural splendour and suffered under the ravages of war.
Evidence also suggests that there was a strong Mongoloid presence as well.
Soon after, in the 5th and 6th centuries B.C. came the Aryans from Central Asia and the Dravidians from Western India. Then came the Guptas, Palas, Senas, who were Buddhist and Hindus. From the 13th century A.D. the Buddhist and Hindus were swamped by the flood of Muslim invaders and the tide of Islam upto l8th century. Sometimes there were independent rulers like the Hussain Shahi and llyas Shahi dynasties while at other times they ruled on behalf of the imperial seat of Delhi. British political rule over the region began in 1757 A.D.when the last Muslim ruler of Bengal was defeated at Palassey.