Of all the issues standing in the way of peace between Israel and the Palestinians, from Jerusalem and refugees to borders and water rights, security has always been considered to be among the easiest to solve, if not the easiest.Yet it is precisely the matter of security arrangements that has become the main obstacle preventing headway in the talks taking place under the orchestration of US Secretary of State John Kerry.Security and borders have always presented a dilemma.Israel has traditionally, and justifiably, refused to discuss borders before settling the issue of security. That is because the vigor of security guarantees in many ways determines the contours of the borders. Agreeing on borders before security creates the risk that the Palestinians will pocket concessions on borders and then refuse to accommodate Israel’s security needs. Palestinians, meanwhile, have balked at discussing security before agreeing on borders, out of a feeling of uncertainty regarding how precisely their future state will look on the map.To his credit, Kerry has managed to convince the Palestinians to focus first on security arrangements, particularly in the Jordan Valley, with the understanding that a Palestinian state will be based on the 1949 armistice lines with land swaps to accommodate settlement blocs. Retired Marine Corps Gen. John Allen, the former commander of US troops in Afghanistan, was tasked with formulating a solution that could answer Israel’s security needs without compromising Palestinian sovereignty.Allen has reportedly accepted the idea that Israeli forces must remain on the ground in the Jordan Valley after the signing of a peace agreement, at least in the short term.Never before has Israel asked America, or any other country for that matter, to do its fighting for it. First, such an arrangement would run counter to the premise of Zionism, which entrusts Jews for the first time in nearly two millennia with responsibility for their own fate.Also, seeing American soldiers risk their lives to protect Israel would risk undermining the special relationship that Israel and American have long had, which in large part is based on the understanding that Israel fights its own battles. And history has shown that international forces such as the UN are inherently unreliable. The Six Day War and south Lebanon provide two examples of how such international forces are ultimately ineffectual. Unfortunately, the Arab League on Saturday made Kerry’s job that much harder when its secretary-general, Nabil Elaraby, agreed, in consultation with Palestinian Authority President Mahmoud Abbas, that not a single Israeli soldier would be allowed to remain on the ground in a future Palestinian state.Israel has many concerns about Allen’s plan. How many Israeli troops will be allowed to patrol the border with Jordan? Where will these troops be allowed access, at border crossings or along the entire border? How long will these troops be allowed to remain? Who will decide when they must leave and according to which criteria? No less critical is the fate of the Jewish settlements in the Jordan Valley. This area makes up about 6 percent of the West Bank. If Israel retains it the Palestinians will demand an equivalent land swap inside the Green Line.This clash over security arrangements illustrates once again the tremendous obstacles to be hurdled by Israelis and Palestinians on the way to hammering out a peace agreement. Though many advocates of a two-state solution claim that the conditions for a final-status agreement are clear and that everyone understands what the final deal will look like, the reality is much more complicated.Even a relatively “easy” issue like security arrangements has turned out to be a potential spoiler. And the sides have yet to grapple with the truly complicated issues of Jerusalem and refugees.As Kerry prepares to return to the region, this time reportedly with a framework agreement in hand, he faces serious challenges. Attaining a two-state solution to the conflict is a cardinal Israeli interest, as it would ensure that Israel remains both Jewish and democratic. We wish Kerry success. Israel, however, has legitimate security concerns.Convincing the Palestinians and the Arab League to address these concerns will be no easy matter.