Sentence:  That bitter rivalry -- between Thaksin's supporters, known as the Red Shirts, and the royalist elites, known as the Yellow Shirts -- has been a hallmark of politics for the past 20 years, with deadly street protests a common occurrence. Friday's announcement signals a surprise <WSD>marriage</WSD> between the two sides, with Ubolratana having the power to break that cycle. 
Meaning of the word marked with <WSD> tags:  A close union. (from 15th c.<ref name="etymonline"></ref>)