Hii!
Here are a few points on the question you mentioned, which you can elaborate in 250 words.
Habitat destruction is a global threat because, everything is interlinked on Earth. If a habitat Is destroyed or fragmented, it's carrying capacity will decrease. It will not be able to support the lives of no. of species of plants and animals which it used to support earlier. This in turn, will destroy those species of plants and animals due to lack of proper food and resources and breeding grounds. This will them effect species dependent on those species and the cycle will go on, eventually destroying every thing on Earth. Humans too, come under this and the cause of habitat destruction is human only. So, eventually, it becomes a global threat.
Hope this helps.
Good luck!