The Orc Empire is a perfect example of backlash. As the leader hoping to establish an alliance, they are now set up to endure the most brutal social backlash.
Perhaps all the races on the continent would want to lend them a hand. However, in the face of the Humans' firm stance, the endurance of others appears to be somewhat lacking.
This is the aftermath of poor interpersonal relations; no species is willing to lead an effort to save the Orc Empire against the Humans.
Everyone is now calling for peace, and the so-called pressure they apply is, at best, like the Dwarves and Elves announcing: a ban on selling weapons to the Humans during the war.
Or perhaps going a step further, like the Half-Orcs and Savages, directly suspending trade with the Humans.
Under the self-sufficient feudal economy, such slight pressure is clearly not intimidating to the Human Alliance.
If "trade ban" were replaced with "war threat", the situation would certainly look different.