Actually, Texas is another good example. In fact, all of Manifest Destiny.

From that entry, though:

Active negotiations led in 1846 to a treaty, by which the republic of New Granada (consisting of present-day Panama and Colombia) granted the United States transit rights across the Isthmus of Panama in return for a guarantee of the neutrality and sovereignty of New Granada.

...

The Hay-Herrán Treaty, signed (Jan., 1903) with Colombia, would have given the United States a strip of land across the Isthmus of Panama in return for an initial cash payment of $10 million and an annuity of $250,000, but the Colombian senate refused to ratify it. An insurrection, involving Bunau-Varilla and other proponents of the canal as well as the regional population, was encouraged by the United States. Panama rose in revolt on Nov. 3, 1903, declaring itself independent of Colombia. Invoking the treaty of 1846, the United States sent an American warship to Panama, and its presence prevented Colombian troops from quelling the outbreak. The new republic was formally recognized three days later, and on Nov. 17 the Hay–Bunau-Varilla Treaty was signed, granting to the United States, in return for the same terms offered Colombia, exclusive control of a canal zone in perpetuity, other sites necessary for defense, and sanitary control of Panama City and Colón. Colombia’s efforts to secure redress for the loss of Panama later resulted in ratification of a treaty (1921) by which the United States paid Colombia $25 million, and Colombia recognized the independence of Panama.

So the US decided they wanted Panama to build a canal, fomented revolution in Panama, and somehow claimed rights to have a warship in the area, preventing the rebellion from being quelled, based on a treaty with a country that no longer existed that stated that the US couldn't intervene.

And I think that understates the case.