The historical dispute centres on the Volhynia massacres between 1943 and 1945. Poland says Ukrainian nationalists killed around 100,000 Poles during the violence, while thousands of Ukrainians were also killed in retaliatory attacks. Tensions over the issue increased after Ukrainian President Volodymyr Zelenskyy named an army unit after insurgents linked to the massacres. Polish president Karol Nawrocki responded by stripping Zelenskyy of a major Polish honour in June.