External as in not something caused by the black people. If it's being inflicted on them it must be coming from outside the group.
How can it be a black problem?
It was explained to you already. But I am happy to explain it to you again.
Black people are about 13% of the US population. Black trans people are therefore presumably around 13% of the US trans population.
However, much more than half the trans people murdered in the US are black (20/26 so far this year, if I'm recalling correctly). So black trans people are getting murdered disproportionately to trans people of other races.
Most murders are intraracial, and most murderers are men. Therefore, it is likely that the people murdering the majority of these black transpeople are black men.
People -- almost certainly black men -- are murdering black transpeople at a grossly higher proportion than transpeople from other races are murdered (probably by men from their own racial group).
Therefore, the black community has a particularly violent transphobic response to the existence of trans people.
How do you intend to address the black community to resolve this problem?