When Robert headed north in late 1307, the war became a civil war.
This raises the question – why was there so much opposition to Robert’s kingship from within Scotland.
Some answers to these questions can be found in the Competition for the vacant crown in the early 1290s. The main competitors were John Balliol and Robert Bruce (the future king’s grandfather). When Edward I eventually decided the case in favour of John Balliol, the Bruces remained aloof, and avoided recognition of John. When John with his Comyn advisors rebelled against Edward, the Bruces “flip-flopped” between support of Edward and sufficient support of the “Scottish” cause, to maintain the credibility of their claim to the throne. In contrast, from the start of the war with England to their final submission in 1304, the Comyn party had consistently supported the Scottish and Balliol cause. Another significant event during 1304 was the death of Robert’s father, and passing of the claim to the throne to him. The following year saw the capture and execution of Wallace.
There are various legends regarding what happened next, but it is an established fact that Robert met John (Red) Comyn at Greyfriars Kirk in Dumfries, and that there was a violent disagreement which resulted in the murder of John Comyn and his uncle, by Robert and his supporters. So he alienated, the Church, Edward I, the Comyns and their allies, at a stroke. With no other options left Robert was crowned King of Scots on March 25th 1306 at Scone. One of the great ironies was that he was crowned by Isabel of Fife, the wife of John Comyn Earl of Buchan.
An interesting site dedicated to Isabel is: http://www.geocities.com/isabel_fife/index.html
As mentioned, in an earlier post, the year following his coronation was a disaster, but now following his successes against the English he was taking the war to his Scottish enemies.