What does "the second Apocalypse" mean? WW2?

I love polish literature. When I read a poem(in English translation) by Zbigniew Herbert I saw a line "our former allies at the time of the second Apocalypse "(or "they were our allies from the time of the second Apocalypse") . I can't understand what does "the second Apocalypse" mean.

The poem's name is "Report from the Besieged City". The context is

and so in the evening released from facts I can think
about distant ancient matters for example our
friends beyond the sea I know they sincerely sympathize
they send us flour lard sacks of comfort and good advice
they don't even know their fathers betrayed us
our former allies at the time of the second Apocalypse
their sons are blameless they deserve our gratitude therefore we are grateful

( or another english transtion
then in the evening freed from the facts I can meditate
on ancient questions remote ones for instance about our
allies across the sea I know they feel sincere compassion
they send flour sacks encouragement lard and good advice
they don't even know it was their fathers who betrayed us
they were our allies from the time of the second Apocalypse
the sons are blameless deserve gratitude so we are grateful )

Anybody can help me to understand?

I think 'second Apocalypse' = Second World War

Or, it might mean "Dzień Sądu" = Judgement Day, Day of Judgement

=Poland under Martial Law


=USA and UK betrayed Poland after World War II

I read a book "A Concise History of Poland" last week.And I suppose Astoria and milawi were right. Thank you all so much. The poem was finished in 1982, so I think "the Besieged City=Poland under Martial Law" was right, too. Thank you Astoria~