So this is why Adama was so willing to accept the news of war in the pilot episode, while Tigh was incredulous and assumed it was a joke. Deep down, for some time, Adama had been afraid the Cylons were coming.

I think Cavel would have started it anyway this just gave him more fuel to convince the others

"Sooner or later, the day comes when you can't hide from the things you've done anymore."

I wish we saw more of the Valkyrie. It’s a beautiful ship.

"Sometimes surviving can be its own death sentence."
Words I live by.

I was surprised to retroactively recognize Bulldog as Carl Lumbly, who would, decades later, play Isaiah Bradley in Captain America: Brave New World.

the music in this scene nails Adams's feeling of regret perfectly

No, Adama's mission wasn't the spark that set it off. This, it seemed more like the Cylons were expecting it because they didn't detect anything close to the armistice line for years, then out of nowhere this stealth ship is detected almost immediately? I'd wager they had the whole mission profile before they even jumped to the line.

Consider this.  That the reason the Cylon's own stealth fighter was able to jump in, engage the Stealth Star, and jump out the way it did, was because the Colonial Defense net was already compromised, and they knew they were coming, as well as had codes to enable them to see a Colonial stealth ship.   Given the execution, that is the only thing that makes sense.  The only other option is that the Admiralty sent another Stealth ship in to damage the Stealth Star and draw a response to confirm that they were still there.  

Also keep in mind that the incident not only confirmed that they were still out there, but it also confirmed that the Cylons have some pretty advanced tech on their side.

The Cylons had infiltrated the Twelve Colonies at least a year before Adama's mission. The fleet and stockpile of weapons had to have taken at least a decade to build. Adama did not start the war.

This was on President Adar and the Cylons, not Adama.

They should’ve brought Bulldog back, unless I’m wrong, he just kind of disappeared from the show, he could’ve come back at the end of season 4, make some sort of last mission under Adama

Ironically, provoking the war then would have worked in the Colonies' favor, since the Cylons hadn't totally compromised their systems yet.

Truly outstanding acting. They all show the gravity of their decisions. Especially Adama.

They waited until after Adama had served a full tour commanding Galactica to attack though.  It wasn't like either side was just waiting for the right moment to strike.  Neither side was ready so both sides kept building their war machines.

No, Cylons already had spies in the camp, preparing for the war. Why build up huge military armada if they weren't going to attack. In the first episode it said they had infiltrated every Battlestar. No, the Cylons had already decided on a preemptive strike on the home worlds.

No. Saul Tigh, a cylon, was already with working for Adama and they've known each other for quite a while. That means the Cylons already set in motion the events leading to the war beginning with the expulsion of the original 5. In the first episode, a model 6 was already integrated society using Gaius Baltar for access. Other Cylon models were found infiltrating different parts of the fleet and colonies; I assume they also were prepping for war.

Chain of command. He was acting under colour of authority, executing the lawful orders of his superiors.  If this was the precipitating event, responsibility lies with the leadership that assigned the mission.  However :
Saul & Ellen Tigh were decanted & programmed 30 years before the destruction of the colonies.  Six begins her mission two years before the apocalypse.  Building the infrastructure & the fleet to destroy the colonies required time… two years is far too short a span. I believe we can safely assume that Cavill‘s Machiavellian machinations were conceived and implemented decades before Bulldog’s mission from Valkyrie.

So much speculation as to whether this incursion across the armistice line triggered the Cylon attack.  However, the Cylons never mention this incident.  It is possible that it wasn't the Cylons who intercepted Bulldog's stealth ship.  Bulldog is really named John Parker and he is a Black Lectroid, it is possible that his enemies the Red Lectroids could have been the attackers.

What a brilliant episode.