(18731904) Armed conflict between The Netherlands and the Muslim sultanate of Acheh in northern Sumatra .
The Dutch considered the sultanate to be within their northern Sumatran sphere of influence and invaded it. Although the sultan capitulated, the Achinese people engaged the Dutch in a prolonged and costly guerrilla war, which the Dutch were able to win only by researching the area and devising a new "castle strategy" that relied on fortified bases.