Bats could be seen flying around bonfires built for
which ancient holiday?

Central to Samhain

Explanation:

Central to Samhain was a community bonfire of sacred oak branches. The light and warmth of the bonfire attracted flying insects, which in turn attracted bats to the bonfire and the festival.

The correct answer to this open question is the following.

Although there is not a specific attach or context to this question, we can say that Nixon’s ideas about the Vietnam war affected the war going forward in the following way.

After many years of conflict and the presence of the United States troop in Vietnam, American people started to protest and question the participation of the US in the Vietnam War. People did not accept the idea of young Americans dying in a war that doesn't belong to them.

So President Nixon started what was known as the "Vietnamization." This was the foreign policy for the Nixon administration regarding the presence and support of the US in South Vietnam. This policy implied the gradual reduction of the US troops in the war, while the US military would still helping South Vietnam with training, weaponry, and supplies. The Nixon administration considered that South Vietnam had to assume that the war was theirs to fight.