Illustration:Rebecca Zisser/Axios

For a few moments last week it might have looked like the tech industry's very own World War III was breaking out, as Apple briefly kicked iPhone users who work at Facebook and Google off much of their own software as part of a privacy dispute.

Why it matters: Hostilities ended as quickly as they began — but the flareup reminded the world of just how completely, and complexly, the technologies and businesses of these giants are connected.

The most valuable companies in the world — Apple, Google, Facebook, Amazon — mostly stayed in their own lanes as they grew into giants. But now they’re increasingly clashing as their growing ambitions bump into one another.

  • If you understand where these giants clash and where they find common ground, you can begin to grasp how they are shaping our world.

Driving the news: Apple was furious when it learned Facebook was abusing rules governing internal apps and quickly kicked the company out of the program, breaking Facebook's ability to test new apps and use internal iPhone apps.

  • When it became clear Google was doing the same thing, Apple was in a bind. Facebook and Apple have few business ties. But Apple gets billions of dollars per year from Google in exchange for making it the default search engine on iPhones and Mac — an arrangement that Apple CEO Tim Cook has had to defend while promoting the company's strong pro-privacy stance.
  • In the end, Apple briefly banned Google, too — then quickly lifted both sentences.
  • It's not clear how long Facebook's ban might have lasted if Google hadn't joined it in the penalty box.

The big picture: Once upon a time, Amazon was largely a retail store, Apple sold hardware, Google was a search engine, and Facebook was an online social network.

  • None of the companies is confined by those definitions any more. They spill over into one another's territory even as they depend on each other to greater and lesser degrees.
  • Facebook and Amazon, for example, both distribute their consumer apps through the Google Play and Apple app stores.
  • Google, Facebook and Apple all rely to some degree on their products being sold through Amazon, despite each also having tensions with the retail giant.

Google and Amazon had vastly different origins but are increasingly rivals.

  • They compete in cloud computing, advertising and other areas.
  • Amazon is also one of the few companies, outside of China, that has been able to release Android-based devices using its own, rather than Google's, app store.
  • The two companies are now warring in the automated assistant/smart speaker arena.
  • The tension led Google to pull YouTube support from some Amazon devices and sparked a fierce battle over which Google devices get sold on Amazon's virtual shelves.

Amazon and Apple have fought but are finding more common ground.

Google and Facebook together control the lion's share of the online ad business.

  • Their competition has long been masked by the scale of the market's growth.
  • As Facebook faces scandal after privacy scandal, Google has tried, with some success, to keep its head down, although critics point out it has even more data on consumers than Facebook.

Facebook and Amazon have the least interplay among the tech giants.

  • The social network and retail giant have relatively few obvious business ties and competitive conflicts.
  • Facebook apps are available for Amazon devices, and Amazon sells the Oculus VR headset.

History lesson: These relationships have never stood still.

  • Apple and Google, for example, were once so close that Google CEO Eric Schmidt was on Apple's board of directors. Then, after Google introduced Android, the relationship chilled dramatically: Schmidt left the board and a patent war broke out.
  • At one time Apple built a connection to Facebook directly into the iPhone operating system. These days, the companies' CEOs are more likely to trade pot shots over privacy and business models than to work together.
  • Google tried several times to challenge Facebook's dominance of social networking head on, but even its biggest effort, Google Plus, was a flop.

The bottom line: Tension is likely to outweigh cooperation, especially as each of the four companies seeks to convince regulators that the others are the ones in need of reining in.

  • The interdependencies won't vanish, though — so expect more skirmishes like the one Apple fought with Google and Facebook last week.

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