Charles Gullans, in the article "Poetry and Subject Matter: From Hart Crane to Turner Cassity" in Southern Review (1970), notes: 

Many of the poems deal with the aftermath of empire, the impact of European capitalism on the colonies, and in particular the relation of the white and indigenous colored populations.

Gullans also notes: 

Cassity is a white Southerner who has lived for some years in South Africa and who has visited in fact or imagination a large number of the former or still colonial areas of the world. His poems on these areas are a mixture of ironic detachment and satiric ridicule.

Donald Davie's "On Turner Cassity" in the Chicago Review (1983) highlights Cassity's wide-ranging travels and poetic subjects in contrast to Cassity's teacher Yvor Winters (who, according to Davie, would "only with difficulty be lured more than 100 miles from San Francisco"):

Cassity is very much a world-wandering poet, a globetrotter, and although the places that he responds to have something in common (mostly, for instance, they are post-colonial places), still the sheer irreducible variety of visitable places and climates is something brought powerfully home to us as we read Cassity.

Davie described his preference for a poem about Amsterdam:

If I say that I read it as a true and vivid report on one specified place on the globe’s surface, I don’t mean to class it with those rhymed picture-postcards from foreign parts with which our poets, on their Guggenheim years in Europe, regale the folks back home. It is of course a passage intérieur as much as it is a paysage locatable on the map, and a season of the soul as much as it a tourist season, or part of one.  

Yi-Hsuan Tso observes that "Cassity's views of the South are iconoclastic, despite his use of traditional literary forms." Tso describes Cassity's views of southern culture in the New Georgia Encyclopedia Companian to Georgia Literature (2011):

Moreover, in Cassity’s opinion, the meaning of “the South” has broadened and transformed as southerners have traveled, colonized, and suffused new lands with southern regionalism. His poem ‘cartography is an Inexact Science’ accentuates his idea of the syndication of culture, suggesting that geography is defined more by people’s interrelationships and less by space… Cassity’s poetry depicts a postcolonial South whose sin, avarice, pride, and morality unveil themselves in exotic outposts, in the interplay of colonial forces of the past and postcolonial lives of the present.

Tso continues:

Cassity considers himself a southerner yet disagrees with the notion that southernness is merely a “literary convention,” since the latter can no longer describe modern southern life. Other than continuing the myths of a ‘tragic’ and ‘guilt-ridden’ South evoked by Faulkner and other writers, Cassity’s poetry implies that southern writers can and should reinvent their language and subject matter.