Final answer:
The first nation to place itself under UN jurisdiction regarding an internal matter is not explicitly stated, but early UN interventions include the Korean War in 1950 and the partitioning of Palestine in 1947 to create the state of Israel.
Step-by-step explanation:
The nation that was the first to place itself under UN jurisdiction regarding an internal matter is not explicitly mentioned in the provided reference material. However, the UN has been involved in multiple cases where nations sought assistance or were subject to Security Council resolutions. The most prominent early example of UN intervention in an internal matter was the Korean War in 1950, where the UN Security Council denounced North Korea's invasion of South Korea and called upon UN members to help repel the invasion. This incident occurred after the Soviet Union had boycotted UN meetings, which otherwise could have vetoed the intervention due to their permanent seat on the Security Council.
Another notable instance included the UN involvement in the establishment of Israel through the adoption of General Assembly Resolution 181 in November 1947, which recommended dividing the British Mandate of Palestine into a Jewish state and an Arab state.