Complex sentence: Nevertheless, a British force was able to move from Ambala to Karnal starting on 17 May, where they were joined by a force from Meerut under Brigadier Archdale Wilson (who had conspicuously failed to prevent the rebel sepoys' move to Delhi on 11 May).
Split into simpler sentences: Nevertheless, a British force was able to move from Ambala to Karnal starting on 17 May. At Karnal, they were joined by a force from Meerut under Brigadier Archdale Wilson (who had conspicuously failed to prevent the rebel sepoys' move to Delhi on 11 May).