Original sentence: But historiography is ever-changing: in the 1960s and 1970s, many historians claimed that the War of the Triple Alliance was caused by pseudo-colonial influence of the British   who were in need of a new source of cotton due to the United States civil war
Edited sentence: But historiography is ever-changing: in the 1960s and 1970s, many historians claimed that the War of the Triple Alliance was caused by pseudo-colonial influence of the British  who were in need of a new source of cotton due to the United States civil war