board.rb

class Board
  def self.from_file(filename)
    board = new

    File.open(filename) do |file|
      line = file.gets.strip
      board.add_territories(line.split(","))
      file.each_line do |line|
        territory = line.strip
        borders = file.gets.strip.split(",")
        board.add_borders(territory, borders)
      end
    end

    board
  end

  # other code similar to what you had before
end