Complex sentence: At the 2018 Winter Olympics, the delegations from both the host nation South Korea and North Korea will march together in the opening ceremony under the Korean Unification Flag.
Split into simpler sentences: At the 2018 Winter Olympics, hosted by South Korea, the teams from the two Koreas will enter the opening ceremony together. The delegations from both the host nation South Korea and North Korea, will march under the Korean unification flag.