It’s also worth noting that again it was a physical-geography descriptor adopted for the nation. “The Netherlands” was the name given to the lowlying lands, just above sea level and eventually protected by dikes, located along the North Sea coast. After the Reformation and the Dutch Wars of Independence, they were divided into the (Protestant) United Provinces of the Netherlands and the (Catholic) Spanish Netherlands, later Austrian. Following the Napoleonic Wars they were reunited as the Kingdom of the Netherlands, but a struggle in 1830-39 led to the Catholic regions gaining separate independence as Beglium.
FWIW, Luxembourg is attached to the other two as it was historically a piece of the Holy Roman Empire under the rule of the House of Orange, in a union of crowns similar to England and Scotland 1603-1707. It gained effective independence in 1815, losing land to Prussia, lost half its land to Belgium in 1839, became de jure independent in 1866-7, and gained a separate monarch when the last Dutch king, Willem III, died in 1890.