Read the following stanza from Alfred, Lord Tennyson's poem, "The Charge of the Light Brigade":

"Forward, the Light Brigade!"

Was there a man dismayed?

Not though the soldier knew

Someone had blundered.

Theirs not to make reply

Theirs not to reason why,

Theirs but to do and die.

Into the valley of Death

Rode the six hundred.

In a short paragraph, explain what historical events this stanza is referring to.