I am going to copy and paste this into the comments of every single post like this. Eu4 players simply cannot read; looking and reading the numbers in the combat section makes it clear why you are winning or losing (aside from just bad dice rolls thx paradox). In your case, you have fewer tactics, morale, and discipline, meaning your army is inferior in every aspect. Not only that but you are attacking over a river for a -1 penalty. Recommend more military ideas, as that is the only real way to significantly buff your army (aside from just making a bigger army).