One of the earliest significant changes to the culture came with the people's conversion to Islam, most likely due to the influence of nearby Malacca in the 1400s. During this time the people of both modern day Brunei and Malaysia were essentially the same as far as culture is concerned, but in the 1500s the Portuguese arrived to Malacca and many of the powerful Muslim traders there moved to Brunei, forever altering the culture and economy.
With the shift of Muslim traders to Brunei, this swampy region grew dramatically as these traders maintained their trade, while also turning the country into a devout Muslim nation. It was these traders that shifted the economy and way of life from a primarily agrarian society to one based on trade and commercialism. People moved to cities and foods were often obtained through external trade as opposed to solely from domestic growth.
Despite the changes, some were short-lived as Brunei's trade was destroyed by the Europeans and later by the Japanese. The only way Brunei survived was with the discovery of oil, which again vastly altered the culture and way of life in the country. However, the discovery of oil returned the people to their former culture in many ways as the economy was again based on trade as urban growth and modernization measures continued.
The sultans of Brunei used the oil to expand their economy and make the nation one of the wealthiest in the region. It also forced a shift in the culture as nearly all new jobs were in the oil industry, from engineers drilling for oil to traders selling it on the international market. People continued to move from their towns to new oil sites and cities as the people became more educated in order to obtain jobs drilling for and selling this new commodity. Today, Brunei continues this trend as the people are becoming increasingly more educated and wealth, while maintaining their Muslim way of life as Brunei is arguably the most conservative Muslim countries in the entire region.