Why is English the Universal Language in the face of other contending Languages such as Mandarin?

That's really a good question since the number of Mandarin speakers in the world is also huge. First of all, English is not a universal language in the whole world. German, French, Russian, Spanish, and of course, Mandarin, are widely spoken around the world and a lot of world corporate business is carried out in those languages. You may survive using English in those countries where these language are spoken, but you'll never get a descent job there unless you know their language. Second, dominance of English in the contemporary scenario is owing to American economic supremacy - major leading job market is in America and the major MNCs are American, even in the remotest corners of the world. One needs to know English seeking a job in English dominated world market/MNCs or to do business with them. Third, English speaking colonialists have ruled the world for two centuries, leaving the major stakeholders (in politics, business, education, culture) dealing with their day-to-day affairs in English, and seeking the future generations to know English to succeed. And now, a large part of population from those countries have migrated to other parts of the world, where they can be understood only if they speak English. Fourth, major scientific and technological breakthroughs have occurred in the English speaking world, therefore, all the related literature is available only in books in English, and it is still growing. The rest of the world is still lagging behind, and only copying what the English speaking world has achieved. So, why wouldn't English be a major language in the world, and everyone, you and me, the colonized (if not physically, mentally colonized) would seek the language of the colonial power?       

I agree with the detailed answer of Mr. Pradeep Sharma.