If two or more people or groups conspire to do something illegal or harmful, they make a secret agreement to do it. They'd conspired to overthrow the government a defendant convicted of conspiring with his brother to commit robberies I had a persecution complex and thought people were conspiring against me. = plot
If events conspire to produce a particular result, they seem to work together to cause this result. History and geography have conspired to bring Greece to a moment of decision But fateful forces beyond the band's control were to conspire against them. = combine
engage in plotting or enter into a conspiracy, swear together; "They conspired to overthrow the government" act in unison or agreement and in secret towards a deceitful or illegal purpose; "The two companies conspired to cause the value of the stock to fall