Again as with the previous points Fry is not without powerful arguments. He is at his most persuasive when it comes to foreign aid - support already dropping a bit under Truman crashed under the Republican Eisenhower. This arguably reflects though a change in the nature of aid. Aid under Roosevelt served a fairly obvious military
I do think his broader point fails- or rather it in a sense Misses the point. It seems to be based on the notion that buying into the Grand Alliance/ existence United Nations/ NATO/ Marshall Plan necessarily implies the internationalism of the 1950's and 1960's with its large permanent foreign aid budgets, treaties about internal treatment of ethnic groups, agreed international limitations on arms and so forth. It just strikes me the former does not really imply the latter as a logical proposition.
And in fact for example the UN as a body as it was operating in the 1950's received a great deal of scepticism of Dean Acheson perhaps the most important architect of the system If any major foreign policy initiative of the post 40's era was like the earlier form of internationalism it was support for aid and US troops in South Vietnam (which again is not to say one could not logically support the earlier moves and oppose Vietnam-or indeed with more of a stretch vice-versa)-and there the south remained the most "internationalist" part of the United States . It's at least as ridiculous to deny opponents of the Genocide Convention the title of "internationalist" as opponents of the Vietnam War.
Again it strikes me it's perhaps best to think of the 1940's as an era where whether the US was to be integrated into the international state system and binding alliances or not was being decided- with by the early 1950's a huge consensus ( even the likes of Robert Taft accepting this) that it was. The South was a leading light for all these measures . McCarthy's personal appeal can in a sense be seen as a reflection of these debates and the Confederacy again was rather resistant to it (every confederate Senator voted to condemn McCarthy-the only Democrat who managed to absent himself was John F Kennedy of Massachusetts-whose Democrats as well as JFK's dad had been very dubious about aid for Britain).
From the early 1950's onwards the debates have been very different-and in my opinion internationalist is the wrong way to discuss them very few US politicians -there is the odd exception are opposed to the internationalist paradigm I've outlined above. The differences have come down very broadly down to two types. Firstly whether to support the use of military force where the South has remained about the most enthusiastic region in the United States (with the odd exception ) . Examples would include the Vietnam War, The first Gulf War and the second Gulf War. Secondly whether the US should agree to treaties or agreements that limit it's actions and/or internal behaviour / and or requite the US to give some resource. Examples of this would include the Panama Canal Treaty, the various test ban treaties,the genocide convention and Detente with the Soviets.
Here the South has been a lot more sceptical even hostile(and after all as already suggested it's opposition to agreements that effect internal policies e..g the genocide convention can be linked to it's anti-imperialism of the early 20th century) . It's perhaps notable that those wars the south has been most relatively sceptical of (for example Kosovo) have been those that have been sold most in strictly humanitarian ways-and in the US obeying an international system (however ridiculous you may feel that is as a representation of the reality of these wars).
All these debates have happened in a context where the international system set up in the 40's has been a given . The rare deviations have been fairly fringe (the most notable being George McGovern the Democratic presidential candidate's desires to withdraw many troops from NATO) and partial-McGovern was a big fan of the UN and foreign aid , while most Right wing Republicans who support withdrawal from the UN are big fans of NATO. This commitment could be seen as early as the early 1950's where the South was even more opposed to General MacArthur's firing than the rest of the United States.
Indeed looking at realignment over foreign policy in the United States-one could say that what has happened (in small part- domestic politics has a ton to do with this) has been the hawkish South has allied with the north more anti commitment form of nationalist sentiment (a major force in "isolationism) into a new "conservative" school of internationalist politics. Whatever this is it is not isolationism-but rather one of the heirs to the interventionist of the 1940's.