Bio withdrew because they were significantly losing the war, and withdrawing gives a HUGE advantage in acres. In an even war, whoever withdraws is guaranteed to gain significantly, so kingdoms that don't care about winning have a massive advantage (side note, this makes the war win charts completely irrelevant) From the KD page it didn't look to me like bio would have started losing acres immediately had they continued, nor was the war fully unwinnable, but they were smart to get out at a good moment.