International Relations studies the dynamics between nations. It is multidisciplinary meaning it focuses on political, historical, and economic skills to understand the bonds and tensions between different countries.
According to UCAS, the average offer for a History course at UK universities is ABB - HOWEVER - this will differ depending on the university you apply to.
UCAS: https://www.whatuni.com/degree-courses/search?subject=international-studies
USEFUL SUBJECTS TO HAVE STUDIED: History/Economics/Politics/Philosophy/Humanities/English
University Subject Guide: https://www.thecompleteuniversityguide.co.uk/courses/search/undergraduate/international-studies?qualification=undergraduate
Careers: https://www.prospects.ac.uk/careers-advice/what-can-i-do-with-my-degree/international-relations