In the 19th century, Cuban sugar plantations became the most important world producer of sugar, thanks to the expansion of slavery and a relentless focus on improving the island's sugar technology. Use of modern refining techniques was especially important because the British Slave Trade Act 1807 abolished the slave trade in the British Empire (with slavery itself being abolished in the Slavery Abolition Act 1833). The British government set about trying to eliminate the transatlantic slave trade. Under British diplomatic pressure, in 1817 Spain agreed to abolish the slave trade from 1820 in exchange for a payment from London. Cubans rapidly rushed to import further slaves in the time legally left to them. Over a 100,000 new slaves were imported from Africa between 1816 and 1820. In other words, 100,000 African people were kidnapped and forced into slavery. "In spite of the new restrictions a large-scale illegal slave trade continued to flourish in the following years.