[3] After the Civil War, Cushing negotiated a treaty with Colombia to give the United States a right-of-way for a trans-oceanic Canal.

He helped obtain a favorable settlement of the Alabama Claims, and as the ambassador to Spain in 1870s defused the troublesome Virginius Affair.

In 1843, Cushing was appointed by President Tyler to be commissioner and United States Ambassador to China, holding this position until March 4, 1845.

[5] With the goal of impressing the Royal Chinese court, the Cushing mission consisted of four American warships, loaded with gifts that exalted scientific wonders including revolvers, telescope, and an encyclopedia.

His arrival at Macau in February 1844 created a local sensation, but the Chinese government was reluctant to designate another most favored nation.

In the following years American trade with China grew rapidly, thanks to the high-speed clipper ships which carried relatively small amounts of high-value cargo, such as ginseng and silk.

The popular Chinese reaction was mostly hostile, but there was a favorable element that provided a base of support for American missionaries and businessmen.

By 1850–64, China was enmeshed in the Taiping rebellion, a civil war which caused millions of deaths; foreign trade stagnated.

[5] He served in the Army during the Mexican War first as colonel of the 1st Massachusetts Volunteer Regiment, of which he was placed in command on January 15, 1847.

He was again a representative in the state legislature in 1851,[5] was offered the position as Massachusetts Attorney General in 1851, but declined; and served as mayor of Newburyport in 1851 and 1852.

He was later appointed by President Andrew Johnson as one of three commissioners assigned to revise and codify the laws of the United States Congress.

[13] Radical Republicans in the U.S. Senate immediately challenged Cushing's loyalties on account of his earlier close personal rapport with Andrew Johnson and his alleged pre-Civil War Copperhead sympathies.

Their feelings of distrust turned into all out opposition to his confirmation when a (non-political) letter that Cushing had written in 1861 to President of the Confederacy Jefferson Davis was found and made public.

The Caleb Cushing served during the American Civil War and was destroyed by Confederate raiders during the Battle of Portland Harbor on June 27, 1863.