Complex sentence: The doctrine, however, met with tacit British approval, and the British Royal Navy mostly enforced it tactically, as part of the wider Pax Britannica, which enforced the neutrality of the seas.
Split into simpler sentences: The doctrine, however, met with tacit British approval. The British Royal Navy enforced it tactically as part of the wider Pax Britannica, which included enforcement of the neutrality of the seas.