When I started reading for myself, I was voracious about it. The Lord of the Rings series was a huge favorite. I pored over them. Something about the bravery and self-sacrifice enthralled me to the point that I read the entire thing aloud to my little brother (with a few canny deletions of endless descriptions of forests). At about age ten, I discovered the Sherlock Holmes mysteries, and I've been obsessed with those ever since. It turned out that hero stories are my mojo.
We grew up in the Pacific Northwest, so we pretty much had free rein of the neighborhood. My parents were always careful, but the town was safe, so we put pennies on railroad tracks to flatten them and sailed Lego men through dyke tunnels and fostered families of mice we found in the meadow. If we weren't reading tales of adventure, then we were out running amok imagining our own.
I'm hugely gratified that the book seems layered. The technique is simply one of character relevance. Did the event affect my character Tim? Put it in. Is it peripheral history that fails to engage him emotionally? Skip it. Does it matter to him what this particular street looks like? Include it. Does he care when that building over there was constructed? No, so don't narrate that information. Timothy likes creating word pictures and he's a bit dazzled by his city (at the same time he's disgusted by it), but I try my best never to put words in his mouth that don't belong there. If I've somehow achieved balance by being (to my mind) massively unbalanced on the side of character, then hallelujah and pop the champagne.
Anyone can do this with practice, diligence, a dash of creativity, and a mild case of OCD, by the way. It's about finding primary sources. Diaries, satires, newspapers. The key is to be omnivorous. When I'm researching by reading a newspaper from 1845, I don't just write down the headlines. The headlines are often immaterial. I record the advertisements, the concert listings, the society gossip, the slang expressions, the ins and outs of everyday life. It isn't difficult, just time-consuming.