Why did the British not have full support of the French in the Somme?

The British did not have full support from the French during the Battle of the Somme primarily due to the heavy toll that the French army had already experienced in earlier battles, particularly at Verdun. The French were focused on their own defensive efforts and were stretched thin, making it difficult to commit additional resources to the Somme offensive. Additionally, there were strategic disagreements between British and French commanders regarding the overall military approach, leading to a lack of cohesive support for the operation.