Complex sentence: Had the expedition succeeded in its objectives, Spain might have been compelled to sue for peace, but owing to poor organisation and lack of co-ordination with the Portuguese, the invading force failed to take Lisbon.
Split into simpler sentences: Had the expedition succeeded in its objectives, Spain might have been compelled to sue for peace. Owing to poor organisation and lack of co-ordination with the Portuguese, the invading force also failed to take Lisbon.