U.S. History/International relation
QUESTION: Has American long history of Isolationism politicized the role that the US plays internationally to such an extent that it prevents the US from exercising more cooperative approach to International Affairs
I have to disagree with your premise. Conventional wisdom is that America was highly isolationist for much of its history. I don't see it myself. Certainly, US policy kept it from getting involved in the European wars of the 19th century. But during that time the US was not remaining uninvolved in military affairs. It was busy conquering North America, fighting a series of wars against the Native Americans. It also took a huge portion of Mexico to make it part of the US as well. America was also highly aggressive in International trade, with Yankee traders going all over the world involved in US trade. US warships protected American merchant vessels around the world, beginning in 1801 in the Barbary wars and continuing ever since.
Already by the 1890's, the US was building a large aggressive navy to challenge the world. The US aggressively moved to flex its muscles around the world, taking colonies in Puerto Rico and other islands in the Atlantic, as well as the Philippines and other islands in the Pacific. That hardly seems isolationist to me.
Certainly since WWII, which was more than 70 years ago, the US has been the dominant international player on the world stage. It has been deeply involved in Europe, the middle east, Asia and around the world. I see nothing that indicates any hint of isolationism.
Even if you consider the US to have been isolationist for some period of time, I don't think that would be the cause of politicization of international affairs. I also don't think it is the cause for the US lack of a cooperative approach to international affairs.
In my view, both can be attributed to the fact that the US dominates in terms of military might. The US spends more on its military than nearly all other countries in the world put together. It simply does not need the cooperation of allies because it has sufficient military power and technology to crush any other country without the assistance of any allies.
Similarly, because the US so dominates the world in terms of its military that no other country or entity poses any sort of threat to US survival now or in the foreseeable future. Sure, things will change over time, but for now the US has no serious threat beyond very limited surprise attacks. Because there is no serious threat to its survival (like there was during WWII for example) there is no need today for the political forces in the US to come together and unite against a common enemy. Political factions can afford to bicker and second guess each other over what policies to pursue. They don't put aside their difference for a united policy because there is no immediate need to do so.
I hope this helps!
---------- FOLLOW-UP ----------
QUESTION: Does theorizing about the state ans international affairs assist in the practical understanding of external relations?
I am not sure I understand what you are asking in your follow up. If you are asking does theorizing about other countries and how they might approach international affairs help with a practical understand, the answer is sometimes yes and sometimes no.
Any state actor would want to guess how others might react to certain policies or events. Since we often cannot just ask our enemies how they would react, we must theorize based on past actions, how we might react in their situation, or how honest they might be in their rhetoric. Through these, we might theorize how a foreign actor would behave.
So theorizing might give us a practical idea of a foreign country's reaction to something. However, such a theory may be error prone and is not a guarantee of a particular outcome. Frequently, leaders rely too heavily on such theories and end up miscalculating results, often leading to disaster.
I hope this helps!