Often called one of the seven modern wonders of the world, the Panama Canal splits the continents of North and South America and launched a new era in global commerce when it opened in 1914.

President Donald Trump has called for the US to retake control of the Panama Canal unless the cost of passage for naval and merchant ships is slashed. Trump’s refusal to rule out the use of force is a throwback to the 19th century era of gunboat diplomacy.

During Monday’s inauguration, Donald Trump repeated his threat to retake the Panama Canal. The United States controlled the waterway since the early 20th century, but in 1977 President Jimmy Carter signed a landmark treaty to give Panama control of the canal.