The emancipation proclamation can be seen as a diplomatic document because it made it hard for the foreign nations to recognize and support the confederacy.
Explanation:
The emancipation proclamation was issued by the President Lincoln in the United states of America which made all the slaves in the region which were in rebellion against the United States.
This was in favor of the slaves to set them free. This made it tough for the foreign nations a little hard to recognize the confederacy among the nations. Thus making it a diplomatic document.