where a player who feels vulnerable tries to become too expensive to be removed while remaining a threat to harass other players. The objective of this strategy is to avoid early defeat. A player using this strategy might remain in the game all the way to later stages and then mount an attack on the weakest player and start a chain elimination to remove one player after another to win the game. The player who uses this strategy is called a "turtle". The term was popularised in real-time strategy games where a player creates a defensive perimeter or a turtle shell around the base of operations. Solutions to counteract this strategy using cooperation have been proposed. Alliances The rules of Risk neither endorse nor prohibit alliances or truces. Thus players often form unofficial treaties for various reasons, such as safeguarding themselves from attacks on one border while they concentrate their forces elsewhere, or eliminating a player who has grown too strong. Because these agreements are not enforceable by the rules, these agreements are often broken. Alliance making/breaking can be one of the most important elements of the game, and it adds human interaction to a decidedly probabilistic game. Some players allow trading of Risk cards, but only during their turn. This optional rule can make alliances more powerful. Attack and defense Capturing a territory depends on the number of attacking and defending armies and the associated probabilities. In a battle to completion, a player who has more armies (even just one more) has a significant advantage, whether on attack or defense (the number of attacking armies does not include the minimum one army that must be left behind in the territory). Defenders always win ties when dice are rolled. This gives the defending player the advantage in "one-on-one" fights, but the attacker's ability to use more dice offsets this advantage. It is always advantageous to roll the maximum number of dice, unless an attacker wishes to avoid moving men into a 'dead-end' territory, in which case they may choose to roll fewer than three. Thus when rolling three dice against two, three against one, or two against one, the attacker has a slight advantage, otherwise the defender has an advantage. There are online tools available to compute the outcome of whole campaigns (i.e. the attacking of several territories in a row). RisiKo! is a variant of the game released in