Languages of Belgium
Dutch is the official language of the Flemish Community and the Flemish Region (merged to Flanders) and, along with French, an official language of the Brussels-Capital Region. The main Dutch dialects spoken in Belgium are Brabantian, West Flemish, East Flemish and Limburgish. All these are spoken across the border in the Netherlands as well, and West Flemish is also spoken in French Flanders. Much like English, Flemish dialects have adopted much more French and other Romance vocabulary through mutual cultural exchange throughout history when compared with other Dutch dialects and as such they are not always readily intelligible for Dutch speakers outside Flanders. Words which are unique to Belgian Dutch are called "belgicisms" (as are words used primarily in Belgian French). The original Brabantian dialect of Brussels has been very much influenced by French. It is now spoken by a minority in the Capital region since the language of most inhabitants shifted during the Frenchification of Brussels.
Partition of Belgium
The main reason for Brussels being mainly French-speaking was the low social prestige of the Dutch language in Belgium during the 19th century and the severe discrimination of both Dutch as a language and of the Flemings. French was, at that time, the language of the administration, government, culture, law and education. From 1880 onwards, more and more Dutch-speaking people became bilingual and passed only French on to their children, resulting in a rise of monolingual French-speakers after 1910. Halfway through the 20th century, the number of monolingual French-speakers carried the day over the (mostly) bilingual Flemish inhabitants. Only since the 1960s, after the fixation of the Belgian language border and the socio-economic development of Flanders was in full effect, could Dutch stem the tide of increasing French use.