As of the end of the first quarter of 2017, the largest market capitalization of the largest companies that are headquartered in the United States were in order: Apple, Alphabet (Google), Microsoft, and Amazon. All of these companies are of fairly recent vintage, of which, for many Americans, upon their birth, these companies did not even exist. This signifies that in the last generation, hi-technology represents the new "go-go" companies of the present age, and while things do change and the future is unknown, they certainly seem poised to continue their dominance for a lot of reasons.
For instance, each of these behemoths dominates its particular niche within the hi-technology field, to wit, as reported by ibtimes.com in regards to Apple that its iphone share represents: "…93 percent of the handset industry’s total measurable profits." As for Alphabet, as reported by searchenginejournal.com, Google's desktop search percentage is at an incredible 79.88%. In Microsoft's case, as reported by extremetech.com, Microsoft has "…89.23% of the OS market." In regards to Amazon, as reported by digitalcommerce360.com, Amazon accounts for: "…43% of all U.S. online retail purchases last year occurred on Amazon-owned sites." All of the above, indicates, that each of these companies aren't just large in the amount of their respective market capitalization, but their footprint upon the business world, here and abroad, is absolutely massive, to which, while we can accord their management team, their sales force, and their personnel, plenty of well-deserved kudos, at the same time, one must really wonder, is there any force out there, whatsoever, that can ever knocked them off of their respective perches.
Another thing, probably quite troubling, about each of these hi-tech companies, is that their growth and their market share, has not been solely based upon their organic growth, in fact, each of these corporations, are serial purchasers and acquirers of companies that they either bought out for the synergy of the deal, for the talent, or to co-opt a competitor. As reported by Wikipedia.com, Apple has made 83 acquisitions, including Beats Electronics and Quattro Wireless; Alphabet has made over 100 acquisitions, including Android and YouTube; Microsoft has made 202 acquisitions, including Skype and Hotmail; and Amazon has made over 50 acquisitions, including Audible and Zappos.
A very strong argument could be made, and should be made, that since each of these respective companies, represent the four largest market capitalizations in America, that further acquisitions should not be permitted, unless under the most scrupulous and stringent conditions, as they are each already big enough, and their influence is already far reaching enough. When you are as large as Apple, et al, you already have in your employment the best and the brightest, including the best lawyers, the best accountants, the best deal markers, and the best lobbyists, with the only people holding out against you, being those that relish being independent from big corporations, or simply haven't been discovered by any of these massive corporations yet.
The thing is that while there are absolutely legitimate and sensible reasons as to why larger corporations buy out smaller ones, there are also reasons that are not beneficial to the public and the marketplace, such as the acquisition of competitors so as to stamp out that competition, the "buying" of new talent, the need to jettison growth, the desire to reduce spending money on research and development, the urgency to gain access to critical copyrights, the desire to improve distribution, as well as to lower overhead, and finally the compulsion to please and placate investment bankers and venture capitalists.
What's good for these companies isn't necessarily good for the public, because less choice, often equates to some sort of premium being paid to purchase or use such from these mega-corporations. Not only that, these four mega-corporations, have a combined market cap of over $2 trillion dollars, which equates to an inordinate influence upon the government, upon local and State politics, upon just about every aspect of life that you can think of, for money is a form of power, and concentrated money essentially means that democracy takes a back seat to plutocracy.