What does this mean"Anon Britania droops the pensive head / While round increase the rising hills of dead"?

Question

Anon Britania droops the pensive head / While round increase the rising hills of dead"

What does that mean

its out of the short story to his excellency, general washington

Answer 1

It's a poem from Phyllis Wheatley, an emancipated African American Slave and poet, to General George Washington.

Britannia is the female embodiment of the British Empire.  She (and hence the British Empire) are described here as old and tired and responsible for many deaths in her thirst for power and pursuit of imperialism.

There is a full profile of the poem and its author at Answers.com