The phrase "a main subject of" is correct and usable in written English.
It can be used when discussing the primary topic or focus of a discussion, article, or study.
Example: "The report highlights a main subject of climate change and its impact on global ecosystems."
Alternatives: "a primary topic of" or "a central theme of".
That is to be a main subject of negotiations in Thailand, probably starting next month.
La Sylphide (1836) stated a main subject of the Romantic ballet, the fight between the real world and the spiritual world.
In fact, U.S. intelligence and law enforcement officials have said that sanctions were a main subject of Flynn's conversation with Kislyak on the day that the Obama administration announced a series of punitive measures aimed at punishing Moscow for its meddling in the 2016 U.S. presidential election.
As the 21-year-old leader of the young wing of Britain's far-right British National Party in 2002, Collett was a main subject of the television documentary "Young, Nazi and Proud," in which documentarian David Modell surreptitiously recorded him expressing admiration for Germany under Hitler's rule and criticizing the presence of Jewish people in Europe.
However, ways to revive the moribund peace process were not a main subject of electoral debate.
However, ways to revive the moribund peace process have not been a main subject of electoral debate.
North Korea was already expected to be a main subject for meetings on the sidelines of the Group of 20 economic summit, but the test adds urgency to a widening U.S. campaign aimed at further isolating North Korea.
Force in biology has been a main subject in the field of biomechanics, which deals with the generation of force from biological activities and effects of applied force to biological structures.
Ionospheric trends have become a main subject since the beginning of the 1990s when the study of upper atmosphere trends gained importance in the context of global climatic change (Roble 1995; Ulich and Turunen 1997).
The motives of these students in choosing entrepreneurship as a main subject within a general course of studies are supposedly very different: They range from the compulsory attendance of the subject and the expectation to select a supposedly easy subject to an honest interest and enthusiasm for the issue (therefore the "ambition" is noticeable).
Proto-Uralic did not have specialized voice markers, such as the Indo-European passive; rather, the function of voice was interwoven with topicalization (a way of indicating the main subject of a sentence), emphasis, and definiteness of the subject and object as well as with verbal aspect.
