Excerpt from A History of the Galaxy by Rosh Benno:
When the New Republic was established shortly after the Battle of Endor, it was seen as a shining hope of beacon for civilisation after the tyranny that was the Galactic Empire. The Senate was re-established, along with the position of Chancellor. However the First Order, a remnant of the Empire, was created and their mission was to destroy the New Republic and reinstate the Empire as the major ruling force in the galaxy. They were, however, defeated by the Resistance, which was led by General Leia Organa, former Princess of Alderaan. So the New Republic flourished, for a time, then in the year 97 ABY infighting among the Senate led to a civil war, which was labelled the Republic Wars by many historians. This war was fought between the New Republic and the Loyalists who wished to keep a stricter grip on the galaxy. When the war ended in 102 ABY, there was a power vacuum left by the New Republic's destruction, scattered cells remained across the galaxy but they didn't join together to create a bigger government, and so a man named Janos Varga, with the help of these cells, created a new galactic government, known as the League of Democratic Planets. Instead of a Chancellor as head, there was a President, who was elected to office every five years by the populations of League planets. Janos was the first President, and under his regime order was once again brought to the galaxy. The Jedi Order was also re-established, having been nearly wiped out during the Republic Wars. As of the year 243 ABY, the League is bigger than the Republic ever was and keep the galaxy safe. In the year 242 ABY, however, the Second Sith Empire re-emerged as a dominant force and their violent, expansionist ways are a threat to the League and it's citizens.