Juneteenth is an amazing holiday and it should be better known. It represents the core of why the US is great.
As a white guy not from the South, I had never heard of it before moving to Atlanta and then watching the show Atlanta. They go to a Juneteenth party. The white host is pretty corny and makes his black guests listen to his spoken word poetry. He's sincere but it's a bit much.
So my first experience with it was basically "listen white people, don't be like this guy" which is totally fair but white people should celebrate Juneteenth as well.
Slavery was a crime against humanity and worst of all against our fellow countrymen. It was a barbaric practice that had no place in the world by 1860. It should have been ended long prior to 1865.
Not only was defeating slavery a major achievement, but it took the mobilization of our entire society to get it done. Basically all fighting-aged men in the North served in the war. It was a brutal war of attrition that was only won through combat, combat, and more combat. The United States Army literally stormed trenches over and over against a secessionist slaver army and took massive losses in dead and injured to win. By the end of the war, the Union and especially the US Army basically saw the war as a religious crusade against treasonous slavers ("As He died to make men holy, let us die to make them free, while God is marching on"). Every single American should be proud of that effort and sacrifice.
The Declaration of Independence was our Baptism in freedom and Juneteenth is our First Communion. We could never live up to the promises and ideals of the Declaration of Independence or the Constitution until Emancipation. It was a worthy cause and it should be celebrated by all.