Short answers, pulled from the story.
The Peace of Westphalia in 1648 marked a turning point when European powers agreed to end the Thirty Years' War and established a system where states held supreme authority within their own borders without external interference.
The Montevideo Convention of 1933 established four requirements for statehood including defined territory, permanent population, government, and capacity to enter relations with others.
On the 2nd of September 2015 the court ruled that the TRNC court system operated established by law referencing constitutional foundations while On the 2nd of July 2013 the European Court of Human Rights decided de facto recognition might be necessary for practical purposes regarding civil administrative measures.
A. James published Sovereign Statehood: The Basis of International Society in London through Allen & Unwin during 1986 exploring whether states truly exist as detectable objects and belong instead to a third category called quasi-abstract which has recently gained philosophical attention within Documentality theory.
Peter Katzenstein applied the term semi-sovereign famously to West Germany in his 1987 book Policy and Politics in West Germany describing limitations both internal stemming from federal systems and external arising from NATO alliances or European Community membership.