Thomas Wentworth, now the Earl of Strafford, became a leading adviser to the King. He threw himself into Charles's plans with great energy and left no stone unturned to furnish the new military expedition with supplies and money. The Scots under Leslie and Montrose crossed the River Tweed, and Charles' army retreated before them. In a short time, the invaders overran the whole of Northumberland and County Durham . Charles had to leave the two counties in Scots hands as a pledge for the payment of Scots expenses when he agreed to peace and signed the Treaty of Ripon in October 1640. The impoverished King had to summon another parliament to grant him the supplies which he needed to make that payment; this Long Parliament attacked his Government, impeaching  his chief supporters, Strafford and Laud. It sat until purged in 1648. In the hopes of winning Scottish support, Charles went to Scotland in the autumn of 1641 where he gave titles to Leslie and Argyll, and accepted all the decisions of the General Assembly of 1638 and of the Scottish Parliament of 1641, including confirming the right of the Parliament to challenge the actions of his ministers. He had now withdrawn all the causes of the original dispute, but within a year his disputes with the English Parliament would lead to civil war.
Question: Under how many leaders did the Scots cross the River Tweed?
Answer: 2