The Role of External Supporters
Once an overt struggle has begun, parties not initially engaged may believe there is something to be gained by providing support for either side. This leads states and organizations to become involved in a conflict on behalf of one of the parties already involved. These outside actors are what we call "external supporters."
Protagonists in a fight are seldom isolated. Each has potential allies and enemies that may join the struggle. Disputants seeking assistance from others not yet involved in the conflict may try to portray their actions in a positive light, so as to win over supporters and dissuade external actors from supporting their adversaries. The may also choose strategies and tactics that are likely to generate sympathy and support of potential allies and avoid other tactics which might drive uninvolved parties to the side of their opponent.
Motivations of External Supporters
External supporters may be motivated by a variety of concerns. For example, a supporter may wish to inflict harm and weaken an old foe or win a portion of the spoils that a war victory might bring. A party might lend its support out of an obligation to support its friends or allies, or out of a sense of commonality with one of the sides. For example, American Jews often support Israel, while American Arabs support the Palestinians.
In other cases, the conflict strategies being used may seem so offensive to external actors that they join the struggle to stop these outrageous acts from occurring. (For example, NATO intervened in the Bosnian and Kosovo conflicts because members were outraged at the "ethnic cleansing" taking place.) Alternatively, the actions of one side may seem so admirable that supporters and allies rally to join the cause.
Ethnic groups struggling for autonomy or independence often gain support from members of that same ethnic group in other countries. For example, in the 1970s and 1980s, the PLO organized and supported opposition activity by Palestinians in Jordan, Lebanon, and Israel's Occupied Territories. Similarly, indigenous rights organizations have promoted the establishment of numerous indigenous peoples' movements, provided strategic guidance for their leaders, and pressured governments to respond positively.
Types of Support
The support provided by states and organizations includes financial and military resources, political backing, and moral support. The provision of funds or weapons is meant to provide power to one of the opposing sides and enable its combatants to wage their struggle more effectively. If the other side realizes that it cannot win, such external support may result in an earlier settlement.
Support may also come in the form of sanctions against one's opponent. For example, external actors in support of dismantling the system of apartheid made use of economic sanctions to apply pressure for change in South Africa. . Though it took a long time, the majority white ruling party in South Africa finally realized it could not sustain the struggle against the whole world's negative opinion, and it consequently opened negotiations to end apartheid.
Is Their Role Constructive or Destructive?
External support can be either constructive or destructive depending on the situation and how it is used. If external support equalizes the power in the conflict, the parties may realize that neither can win without enormous costs, and thus agree to negotiate a settlement. (This situation is referred to as "ripeness.") External supporters might then provide resources to help attain a settlement, or to implement one once it is reached. (For example, external supporters of the Palestinians offered a substantial amount of aid to help the fledgling Palestinian state in the Oslo Accords, though this offer was not enough to induce the Palestinians to accept that agreement.)
However, external support also makes it possible that conflicts will be protracted, deadly, and highly resistant to settlement.. If the balance of power between adversaries is equalized, yet neither is willing to admit that they cannot prevail (in other words, that they have reached a "hurting stalemate,") then the conflict is likely to continue longer with the additional aid. In addition, such wars are not likely to end in negotiated settlements unless and until it is in the interest of the external powers. Consequences tend to be particularly tragic in cases where competing powers support different sides in conflict. For example, many local conflicts in Africa, Central America, Asia and the Middle East were sustained and exacerbated during the Cold War as a result of the assistance granted by the U.S. and the Soviet Union to opposing sides.  As a result, it is sometimes the withdrawal of external support that opens possibilities for settlement.
 Louis Kriesberg, Constructive Conflicts: From Escalation to Resolution, 4rd edition, 2012. p. 158-161 <http://www.amazon.com/Constructive-Conflicts-Escalation-Louis-Kriesberg/dp/1442206845#reader_1442206845>. Original citation to page 172 of second edition.
 Ted Gurr, "Minorities and Nationalists: Managing Ethnopolitical Conflict in the New Century" in Turbulent Peace: The Challenges of Managing International Conflict, 177.
 Peter Gastrow, "A Joint Effort: The South African Peace Process" http://www.xs4all.nl/~conflic1/pbp/part1/8-joint_.htm
 Ted Gurr, 178.
 Kriesberg, 168.
By Michelle Maiese