Answer based on context:

Immediately, the Capetian family reacted. On 5 January 1242, Count Alphonse of Poiters called together the Poitevin nobles at Chinon for Easter. The faithful lords, and others less loyal but nonetheless enemies of Lusignan, responded to the appeal.  Although his mother Blanche of Castile had coped with baronial uprisings before and carried on the royal affairs since 1226, with the title "baillistre" , Louis IX decided to go to the assistance of his brother and forcibly take control of the County of La Marche. In April 1242, Louis assembled a force at Chinon that some contemporaries estimated at around 50,000. On 9 May, he marched against the castle of Montreuil-Bonnin, the fortress of Lusignan. After having seizing a multitude of rebel castles, he steered towards Saintes. On 20 May 1242, Henry and Richard departed Portsmouth for Royan and joined the rebelling French nobles, forming an army that may have numbered about 30,000. The two kings exchanged letters, but these resolved nothing. Henry had intentions to regain the past Angevin Empire of his predecessors on the basis that the title of Count of Poitou stills belonged to his brother, Richard. This was not the first war that Henry had waged in France either as he had earlier lead an expedition to France in 1230, however, Henry was convinced that Hugh would provide the necessary support to reverse the lackluster results of the last war. While completing his conquest of lower Poitou, he declared war on Saint Louis on 16 July. On 20 July, the French army arrived at Taillebourg where the inevitable clash took place.

Which country did Louis IX take with force?
La Marche