The Netherlands is a confusing country. After Louise the Pious, the son of Charlemagne, Western Europe was divided into three areas. France and Germany and these two were divided by a territory called 'Lorraine'. The Netherlands at first were part of Lorraine, however, being in the middle meant being attacked from both sides. As a result Lorraine diminished and officially 'The Low Countries' became part of the Holy Roman Empire. The Low Countries were divided into 17 counties/provinces with each having its own Duke Count or Bishop.
Gradually by inheritances most of the territories became the property of the Duke of Burgundy. However, the last of that family, Maria the Rich, married the future Emperor Maximilian and their son married the heiress of Spain.
Because of the Spanish marriage the heir, Philip II of Spain, lived in Spain and regarded The Netherlands only as a territory that provided him with money to pay for his wars. Then his religious intolerance further infuriated the Dutch and the 80 years war started. In the beginning, 1579, the brother of William the Silent made a treaty known as 'the Union of
Utrecht' which combined the seven northerly provinces. In the same year the Spanish regent created the 'Union of Atrecht' which combined the 10 southerly provinces. 

The seven northerly became "The Republic of the Seven United Provinces". However, the most important province of those was the province of Holland and people began to refer to Holland when meaning the republic. Who had heard of Drente, Groningen, Gelderland, Utrecht? It was Holland and Amsterdam that counted.

The southerly provinces were first 'the Spanish Netherlands', then through inheritance "The Austrian Netherlands". After Napoleon the Austrian Netherlands and 'Holland' were combined into the Kingdom of The Netherlands. However, the northern and  Protestant provinces regarded themselves more important and tried to dominate the catholic and southern provinces. As a result civil war broke out and the south went its own way
and became Belgium. The northern part remained the Kingdom of The Netherlands. The Province of Holland is now divided into two provinces 'North-Holland' and South-Holland. North Holland has Amsterdam, the capital of the Netherlands and South Holland has The Hague, the seat of the Government. 

Source: Leo van de Pas