They conspired ________ the leader.

Conspire against - কারো বিরুদ্ধে ষড়যন্ত্র করা।
- They conspired against the leader.

তাছাড়া,
• Conspire (with somebody) (against somebody) - They were accused of conspiring against the king.
• Conspire (together) (to do something) - They deny conspiring together to smuggle drugs.
• Conspire (with somebody) (to do something) - She admitted conspiring with her lover to murder her husband.

- Conspire এর সাথে between, preposition টি ব্যবহৃত হয় না।

Source: Oxford Dictionary