Which Central American canal route was abandoned by France after 22,000 deaths?

Panama. Ferdinand de Lesseps, who had built Suez, began in 1881 with a sea-level canal and no lock system, on the assumption that what worked in flat desert would work through a mountain range in the wettest place he had ever tried to dig. The company collapsed in 1889 in the largest financial scandal of the French Third Republic.

What killed the workers was mosquitoes, and nobody knew it. Malaria and yellow fever were attributed to bad air, and hospital beds were stood in bowls of water to keep ants off - which bred the mosquitoes in the wards. Estimates of the dead run above 20,000. When the Americans took over in 1904 they put a doctor, William Gorgas, in charge of fumigation, drainage and screening, and the death rate fell by an order of magnitude.

The politics were as ugly as the engineering. Colombia refused the American terms, so the United States backed a Panamanian independence movement, recognised the new country within hours and signed a canal treaty with a French agent acting as its envoy days later. The Nicaragua route was the serious alternative and lost partly to lobbying that made much of a Nicaraguan postage stamp depicting a volcano.