Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente. Reserve about 1 cup of pasta water, then drain the spaghetti and set it aside.
In a large skillet, heat the olive oil over medium heat. Add the finely diced onion and sauté for about 5 minutes, or until it becomes translucent. Stir in the pressed garlic and cook for an additional 1-2 minutes until fragrant.
Add the stewed tomatoes, crushed tomatoes, and tomato paste to the skillet. Pour in the chicken broth and stir to combine. Bring the mixture to a gentle simmer.
Add the granulated sugar, dried oregano, dried basil, salt, and black pepper to the sauce. Taste and adjust the seasoning if needed. Allow the sauce to simmer for about 20 minutes, stirring occasionally to prevent sticking.
Once the sauce has thickened slightly, stir in the chopped fresh parsley. Add the cooked spaghetti to the skillet, tossing to coat the pasta evenly with the sauce. If the sauce seems too thick, add a bit of the reserved pasta water until you reach your desired consistency.
Serve the spaghetti marinara hot, garnished with additional chopped parsley if desired. Pair it with a side of garlic bread or a fresh salad for a complete meal.
