文明は今や核戦争に脅かされている。

。

Civilization is now threatened by nuclear war.

Literal

Civilization [topic-は] now nuclear-war [agent-に] is-being-threatened.

脅かされている is the passive progressive of 脅かす (to threaten) — 'is being threatened.' 今や means 'now' with an emphatic, dramatic nuance ('now, at this point in time'). The passive with に marks the agent (nuclear war).