A new book about Facebook's acquisition of virtual-reality firm Oculus has revealed an almost 2,500-word email from Mark Zuckerberg from 2015 detailing his grand vision for AR/VR.Zuckerberg's email was about Facebook's potential acquisition of gaming startup Unity ' a deal which never came off.In the email, he says that Facebook's biggest weakness is "innovation."A new book contains a nearly 2,500-word email from Mark Zuckerberg in which he lays out his grand plans to dominate virtual-reality, TechCrunch reports."The History of the Future," by Blake Harris, tells the "larger-than-life true story true story of Oculus," the VR company which Facebook bought for $3 billion in 2014.The email from June 2015 was reportedly sent from Zuckerberg to then-Oculus CEO Brendan Iribe, Facebook COO Sheryl Sandberg, and six other Facebook execs. It details plans to buy the game-engine developer Unity, a deal that ultimately never materialised.Read more: Unity Technologies, the gaming startup worth more than $3 billion, is reportedly planning to go public in 2020Although only excerpts of the email are available in the books, Harris sent TechCrunch the whole thing. TechCrunch writer Lucas Matney published the letter on Twitter:Facebook mulled a multi-billion-dollar acquisition of Unity, according to @blakejharrisNYC's upcoming book. Here's the 2,500-word email Zuckerberg reportedly sent to key FB leadership where he laid out his grand vision for dominating virtual reality.https://t.co/mMJAf9enO3 pic.twitter.com/HLPuJcaosZ' Lucas Matney (@lucasmtny) February 14, 2019Notably, Zuckerberg says that Facebook's biggest weakness in the face of major mobile platform developers like Apple and Google is "innovation.""An innovative brand comes from building tangible new products," Zuckerberg writes in the email. Since 2015, Facebook has brought out Oculus VR headsets, released its own video-chat hardware Portal, and toyed with building drones to bring internet to remote parts of the globe.Zuckerberg wrote in his 2015 email that Facebook had to be at the forefront of VR/AR to secure a dominant position quickly before its competitors move into the space."Our goal is not only to win in VR / AR, but also to accelerate its arrival," he wrote.Zuckerberg also noted that an acquisition of Unity would have given Facebook a certain amount of leverage against big app platforms."If we own Unity, then Android, Windows and iOS will all need us to support them on [sic] larger portions of their ecosystems won't work. While we wouldn't reject them outright, we will have options for how deeply we support them."Join the conversation about this storyNOW WATCH: Here's how to use Apple's time-saving app that will make your life easier Click here to read full news..