Complex sentence: Schomburgk's initial sketch, which had been published in 1840, was the only version of the "Schomburgk Line" published until 1886, which led to later accusations by Grover Cleveland that the line had been extended "in some mysterious way".
Split into simpler sentences: Schomburgk's initial sketch, which had been published in 1840, was the only version of the "Schomburgk Line" published until 1886. This led to accusations by Grover Cleveland that the line had been extended "in some mysterious way".