NAIROBI, Kenya — THIS was the attack we all knew was coming.

The Westgate mall, which is owned by Israelis, was a glitzy mecca for rich Kenyans and expats, a symbol of Kenya’s newfound decadence. My wife and I went on dates there all the time, catching a movie in a theater as comfy as any in the United States and then dropping $100 for some sushi. After we had kids, we’d take them to Westgate for shopping and ice cream, and it’s where my son Apollo, born and raised in Kenya, rode his first escalator. Westgate, actually, was where I interviewed my first real live Somali pirate (by phone). He was bobbing on the bridge of a hijacked tanker in the middle of the Indian Ocean. I was sitting at a cafe, drinking a banana smoothie.

On Sept. 21, at 11:30 a.m., on a typically bright and pleasant Nairobi morning, Islamist militants with military-grade weaponry stormed into Westgate, turning it into an abattoir. The first of the more than 60 people who were gunned down were sitting at that same cafe where I used to do my interviews, and the steps that I used to trot up holding my son’s hand are now smeared with blood.

For the past seven years that I’ve lived in Kenya, I’ve been following two very different story lines that represent what’s happening in contemporary Africa and that collided that fateful day in Westgate. The first is of the dramatic expansion of Africa’s middle class, now more than 300 million people, and perhaps there’s no better place on the continent to watch this than in Nairobi, where new office blocks are rising above the tin-shack slums, new bistros are popping up all over the place and taxi drivers are getting on Facebook. It’s essentially Africa joining the world.

When I first came here more than 20 years ago, the difference between life in the States and life in Kenya was enormous. There were barely any malls, for instance, and they sold things like yellow plastic jerrycans and roughly machined pots. Now you can get everything here — the latest Macs, frozen yogurt, Old El Paso taco mix — and at Westgate, it was all under one roof.