conspire
v.v. to secretly plan to do something, especially something illegal or harmful. It can also mean that several things happen together to cause a specific result.
v. to act in secret to commit an illegal or harmful act; alternatively, to act in a way that produces a specific, often negative, result. Often used intransitively with 'against' or 'to'.
The two companies conspired to fix the prices of their products.
The heavy rain and the broken bridge conspired to make the journey to the mountain village nearly impossible.
While the two rivals were known to have conspired against the king, the actual execution of the plot was carried out by a third party acting in the shadows.
From Middle English conspiren, from Old French conspirer, from Latin conspirare, conspīrō, from con- (combining form of cum (“with”)) + spīrō (“breathe”).