establishment of diplomatic relations
Formal term used in political and international contexts.
The two countries marked the 50th anniversary of the establishment of diplomatic relations.
Negotiations toward the establishment of diplomatic relations are ongoing.
国交 means 'diplomatic relations' in general, while 国交樹立 specifically refers to the act of establishing them.
外交関係 is a broader term for 'diplomatic relations', whereas 国交樹立 focuses on the formal establishment.
Compound of 国交 (diplomatic relations) and 樹立 (establishment).