The rule that does all the work
Three of the four constraints are ordinary bookkeeping. One per row, one per column, one per region: on their own, those would make a gentle puzzle you could fill in almost mechanically. The fourth constraint is where the puzzle lives. Because no two sentinels may stand adjacent, and adjacency includes the diagonals, placing a single sentinel eliminates up to eight neighbouring cells at a stroke.
That is a large amount of information from one decision, and it propagates. A sentinel in a tight region can rule out the only remaining cells of a row two steps away. Most of the pleasure of the genre is in following that chain - not in the placement itself, but in noticing what the placement quietly forbids.
The deductions worth learning first
Beginners tend to hunt for cells where a sentinel must go. Stronger solvers spend most of their time doing the opposite: crossing out cells where one cannot. The board fills up with negative information, and the positive answers fall out of it almost for free.
Two ideas carry an enormous amount of the weight. The first: if every open cell of a region sits inside a single row, that row’s sentinel is somewhere in that region, so the rest of the row can be crossed out. The second is the same thought reversed - if a row’s remaining candidates all sit inside one region, that region is spoken for. Learn to look for both and most easy and medium boards stop being searches and start being readings.
The squeeze is the third. When a row’s candidates are packed into a narrow band of adjacent columns, any cell in the row above or below that touches all of them is impossible, whichever candidate turns out to be right.
Where the genre comes from
The form is a competition puzzle by origin, and it shows: it is compact, it has no arithmetic in it at all, and it scales in difficulty without ever changing its rules. Puzzle championships have used it for years, and newspapers that carry it sometimes print it under a plainer name describing the non-touching rule.
What it is not is a numbers puzzle. Nothing is added, nothing is counted beyond one. If sudoku never appealed to you because of the digits, this is the same kind of thinking with the arithmetic removed.
One answer, and a route to it that never needs a guess
Every board here has exactly one valid arrangement, and - separately, and more importantly - a path to that arrangement made entirely of named deductions. A board with a single answer can still be a bad puzzle if the only way through is trial and error. Those do not get published.
The difficulty label follows from that: it is the hardest deduction the board actually requires, not an impression of how it feels. An Expert board is genuinely demanding expert reasoning rather than a bigger grid with more cells to fill.
Common questions
Is a star battle puzzle the same as sudoku?
Only in that both are grid logic puzzles with a single answer. Sudoku is about digits and the nine-box structure; this has no numbers in it at all. You place one marker per row, column and region, and the real constraint is that no two may touch.
How many stars go in each row?
One, on every board here. Some variants of the genre use two per row, column and region, which changes the deductions considerably. These are all one-star boards.
Do diagonals count as touching?
Yes, and this is the rule people most often miss. A sentinel blocks all eight cells around it, corners included, which is exactly why one placement tells you so much.