Although anti-slavery efforts became organised in Europe in the 18th century, the slave trade only came to an end in the early 19th century, thanks in large part to English efforts to block shipping to the French during the Napoleonic Wars. Portugal was one of the first countries in the world to outlaw slavery, and did it so in mainland Portugal during the 18th century. The Portuguese government ended colonial slavery in stages with a final decree in 1858 that outlawed slavery in the overseas empire. The gradual pace of abolition was due to the strength of pro-slavery forces in Portuguese politics, Brazil and in Africa, they interfered with colonial administrators who challenged long-established and powerful commercial interests.