At the end of the Warring States period, Qin, the strongest state, was ambitious to unite China, while the other six states, to protect themselves, tended to ally to fight against Qin, but sometimes for various reasons, they fought with each other as well.
One year, the king of State Zhao planed to attack the state of Yan. Hearing this, the king of Yan sent his adviser, Su Dai, to speak to the king of Zhao.
After greeting, Su Dai said the king, "Your Majesty, on my way to your kingdom, I saw a big clam sunning itself at the bank of the river Yi, and a snipe took this occasion to peck the clam's flesh, but no sooner had its long beak reached into the clam's shell, than the clam snapped his shell shut very hard, trapping the snipe's beak inside.
The clam wasn't scared at all and said, "If today you cannot get out, and tomorrow you cannot get out, you will be a dead snipe."
So although the two both knew they would die, if they continued like that, but each was unwilling to let its opponent go until a fisherman came by and snatched up the both of them.
Now Zhao is attacking Yan. It will certainly cause a long war between Zhao and Yan, in which the soldiers of both sides will be killed, and people exhausted. Zhao and Yan are just like the clam and snipe in the story. Your Majesty, I'm afraid the strong Qin will act as the fisherman. I wish Your Majesty could think twice before you act."
The king of Zhao was fully convinced and gave up his plan.
Background And Writer Comment:
This story is from Intrigues of the Warring States (战国策Zhan Guo Ce)
The idiom of A Snipe And A Clam Locked In Combat--Yu Bang Xiang Zheng has the same meaning and usage as his English counterpart "Two dogs strive for a bone, and a third runs away with it" or "When shepherds quarrel, the wolf has a winning game".