intervention (n.)

• encroachment
• entrance
• entrenchment
• impingement
• imposition
• incursion
• infiltration
• influx
• infringement
• injection
• inroad
• insinuation
• intercession
• interference
• interjection
• intermediation
• interposition
• interruption
• intrusion
• invasion
• involvement
• irruption
• mediation
• trespass