How do war crimes and injustices that occur in unstable countries affect us in the modernized first world?

Because alot of the products we use are either made in, or made from materials originating in some of those unstable countries. Instability can also spill over into neighbouring countries, some of which may be allies or economic partners of ours. This being said, you are technically misusing the term First World. While alot of people today use the terms First world interchangably with inustrialised countries, and Third world interchangably with poorer countries, the terms are actually holdovers from the Cold War. First world was NATO and allies of the United States, Second World was the Soviet Union and other members of the Warsaw Pact. Third World referred to countries who were outside the direct sphere of influence of either group. Now as both parties tried to expand their sphere of influence they often backed rival factions that they felt would best serve their interests if such factions came to power. This still goes on to an extent today though without Cold War politics as the motivation.

They don't except injustice does have an affect.

The filthy rich in Hollywood have a strange effect.

They are affected by politically correct injustices to make themselves appear worthy.

It doesn't affect us, although the other countries that are effected could become dangerous to live in.

"injustice" is a cancer to the human condition as a whole... no mater in which "part" it spawns.

See: "September 11, 2001" for an example of how things "over there" can affect us here..

it does not affect us unless those countries possess something such as oil or ore that we need or maybe they have a port ect that makes shipping lanes more assessible

Because these things tend to multiply and spread if not denounced and stopped.