To invade means to enter a place or territory forcefully and with intent to conquer or occupy. In the context of unresolved tensions after World War I, the term reflects the aggressive military actions taken by countries that sought to expand their territories or assert dominance, leading to heightened international conflicts and instability. The period following the war was marked by various nations attempting to assert their power, often through military means, which further complicated diplomatic relations and contributed to the atmosphere of tension and unrest in Europe and beyond.