UCDP and PRIO - conflicts
The UCDP and PRIO annually publish the Armed Conflict Dataset. This is used to count the participation of countries that have been directly involved in conflicts. The underlying definition only considers wars and conflicts in which at least one party to the conflict is a state, and the conflict results in at least 25 battle-related deaths.
Links:
UCDP (Uppsala Conflict Data Program)
PRIO (Peace Research Institute Oslo)