Please answer the following question: Extract the answer to the question from the following context. Question: What caused the three great powers to take such drastic action? Context: After years of negotiation, three Great Powers, Russia, the United Kingdom and France, decided to intervene in the conflict and each nation sent a navy to Greece. Following news that combined Ottoman–Egyptian fleets were going to attack the Greek island of Hydra, the allied fleet intercepted the Ottoman–Egyptian fleet at Navarino. After a week-long standoff, a battle began which resulted in the destruction of the Ottoman–Egyptian fleet. A French expeditionary force was dispatched to supervise the evacuation of the Egyptian army from the Peloponnese, while the Greeks proceeded to the captured part of Central Greece by 1828. As a result of years of negotiation, the nascent Greek state was finally recognized under the London Protocol in 1830.
A:
news that combined Ottoman–Egyptian fleets were going to attack the Greek island of Hydra