What significant engineering project was completed under Roosevelt that connected the Atlantic and Pacific Oceans?

The Panama Canal is the significant engineering project completed under President Theodore Roosevelt that connected the Atlantic and Pacific Oceans. This ambitious project, which was officially opened in 1914, dramatically shortened maritime travel by allowing ships to avoid the long and perilous journey around the southern tip of South America via the Strait of Magellan.

Roosevelt's administration played a crucial role in the construction of the canal after the United States supported Panama's independence from Colombia, paving the way for the U.S. to secure the rights to build and control the waterway. The canal not only facilitated international trade and naval mobility but also underscored the United States' growing stature as a global power during the early 20th century.

The other choices do not fit the context of an engineering project that connects oceans: the Great White Fleet refers to a naval battle fleet that showcased American military power; the Monroe Doctrine established a policy of opposing European colonialism in the Americas; and the Pancho Villa Expedition was a military operation against the Mexican revolutionary leader. These options are significant in their own contexts but do not pertain to the construction of a canal.