It was caused by an improbable concatenation of circumstances.
A complicated concatenation of circumstances.
Word: "concatenation"
different meanings

A wave of settlers.
Troops advancing in waves.
Word: "wave"
the same meaning

The war on poverty.
The "war on terror" is a campaign against terrorist crime.
Word: "war"
the same meaning

Think thin.
Think big.
Word: "think"

the same meaning