Le Marinel's first Congo tour ran from 1884 to 1887. He went out under the International Association of the Congo, the private entity that was the precursor of King Leopold II's Congo Free State - a regime that would become one of the nineteenth century's most notorious examples of colonial extraction and brutality. In 1885, Le Marinel helped define the Bas-Congo border between the new Congo Free State and Portuguese Angola. He then commanded the post at Léopoldville. The young officer returned to Europe in 1887. For a man raised on a farm in the Mississippi Valley, whose childhood German had been acquired from Iowa neighbors and whose French from a father who had adopted Belgium twice, the Congo must have offered a different kind of strangeness. He was fluent in survey, in command, in the mechanics of getting a steamer up a river or a column of porters through bush.

In May 1889, Le Marinel joined Alphonse van Gèle's fourth Ubangi expedition. They left Léopoldville aboard the steamers En Avant and Association internationale Africaine, with a large canoe. At Zongo they founded a base, nearly losing the Association internationale Africaine in the rapids. At Banzyville, 300 kilometers above Zongo, they left sub-lieutenant Léon Busine in command. They pushed further, exploring the Kotto River, establishing the post of Yakoma at the junction of the Bomu and the Uele. When they met, by prior coincidence, a column under Léon Roget and Jules Alexandre Milz coming down from the north along the Uele, the Belgians had answered a long geographical question: the Ubangi and the Uele were the same river system. What the question had never needed answering to the Zande and Banda and Nzakara peoples living along these rivers is a different matter.

In November 1891, Van Gèle handed command to Le Marinel and left for Europe. Le Marinel met Sultan Bangassou - one of the most powerful rulers of the Zande country - and then traveled up the Mbari River, where in September 1892 he established the Bakouma post with Commander Georges Adolphe Balat. He also reached the territory of Sultan Rafaï. The treaties Le Marinel and his colleagues signed with these sultans were, in the Belgian view, instruments of colonial sovereignty. In the sultans' view, they were often instruments of convenience - a way to secure access to European firearms and commerce while preserving local authority. The actual meanings of 'protectorate' and 'territory' diverged across the table. Bangassou continued to rule as Bangassou. His sons and grandsons are still remembered in the modern town that bears his name.

Le Marinel's third tour (1893-1895) brought him back as state inspector of Haut-Ubangi-Mbomou. He commanded expeditions that pushed toward Dar Fertit and the Bahr el-Ghazal - country that interested both Belgian Congo Free State ambitions and the French, who were pushing east from what is now the CAR. The tension between Belgian and French expansion was resolved on 18 August 1894, when the two governments signed a convention establishing the Mbomou River as the border between their colonies. The line Le Marinel helped produce - drawn by Europeans, walked by European surveyors with African porters - is still today the boundary between the Central African Republic and the Democratic Republic of the Congo. Sultans and sub-sultans across this border were told they were now subjects of different empires. Most of them continued doing what they had always done, which was govern the people they had always governed.

Le Marinel went home on leave in 1895 and was assigned to the Ministry of Colonies in Brussels. He held senior posts in the Congo Free State bureaucracy and later the Belgian colonial administration. When the First World War broke out in 1914, he rejoined the army as a captain-commandant of engineers. He died in Edinburgh on 20 November 1914, just months into a war that would reshape the world. Think about his trajectory. An American farm boy turned Belgian officer, drawing borders in a part of Africa that had never asked him to, through a decade in the service of a king whose methods in the Congo would be condemned by his own century. The villages where Le Marinel's treaties were signed are still there. The people along the Mbomou still live across a border he helped create. The Iowa farm where he was born is still there too. There is no obvious connection between these places except the man who moved among them.