UCDP - Uppsala Conflict Data Program/ PRIO - Peace Research Institute Oslo
The UCDP and PRIO annually publish the Armed Conflict Dataset, that contains latest information on conflicts per year. The underlying definition of war only recognises wars or conflicts in which at least one state is involved and which results in at least 25 battle-related deaths. They classify wars into extra state / extra systemic violent conflicts (state against non-state actor outside of existing borders), inter-state conflict (between two states) and intra-state (state against non-state actor within existing borders) and internationalised intra-state conflicts (state aided by other states against non-state actor within existing borders).
UCDP (Uppsala Conflict Data Program)
PRIO (Peace Research Institute Oslo)
Pettersson, Therése and Kristine Eck (2018) Organized violence, 1989-2017. Journal of Peace Research 55(4).
Gleditsch, Nils Petter, Peter Wallensteen, Mikael Eriksson, Margareta Sollenberg, and Håvard Strand (2002) Armed Conflict 1946-2001: A New Dataset. Journal of Peace Research 39(5).