In January 49 B.C., the army of Julius Caesar stood before a bridge crossing the Rubicon River separating the province of Gaul -- where Caesar was governor -- from Italy proper. As governor he had the right to lead an army within his province. But taking it across the river into Italy proper was deemed a challenge to the Roman Senate's authority -- an act prohibited by law and punishable as treason.

Due to the Senate's fear of Caesar's rising popularity among the people for his numerous military victories over tribes in his province, it ordered him to resign his command and disband his army. Caesar could either acquiesce to the Senate's order or cross the river to topple its leadership.

Hesitating on the Gaul side of the river, Caesar offered his men, who by crossing would also be guilty of treason, "Still we can retreat!" All joined him in the crossing.

Once on the other side, Caesar exclaimed, "The die is now cast!"

Today, the idiom "crossing the Rubicon" has survived to mean "passing a point of no return." For Caesar, passing the point that day changed the course of history.

Two millennia later another world leader stands at the Rubicon. A decision will soon be made whether to retreat or cross. The former will ensure peace; the latter most likely will mean war.

On Friday and Saturday, a new round of talks is to take place in Istanbul on Iran's nuclear program, although Iran already is fighting that venue.

On one side of the negotiating table will sit the P5+1, consisting of the five permanent members of the U.N. Security Council (the United States, Britain, France, Russia and China) plus Germany -- all looking to Iran to prove it isn't developing nuclear weapons -- with most vowing to ensure Tehran does not.

On the other side will sit Iran, which insists its program is peaceful, vowing not to terminate it.

Therefore, either one side's vow will be subordinated to the other's or military force will seek to accomplish what negotiations cannot.

In Roman times, it was Caesar who reflected momentarily on whether to cross the Rubicon before doing so. Now, it is Iranian President Mahmoud Ahmadinejad turn.

Should he not agree to international inspections of Iran's nuclear facilities or should he endeavor to delay or prevent any such inspection to buy more time for Tehran, the die will have been cast as he crosses the Rubicon. The onus then will be upon the P5+1, or some of its individual members, as to whether the vow to stop Iran's program will be subordinated to Iran's vow not to.

Based on Iran's track record, we can expect Ahmadinejad to plant the seed that compromise is possible when, in reality, he has ruled it out.

U.S. Secretary of State Hillary Clinton has said about the upcoming meeting, "It will soon be clear whether Iran's leaders are prepared to have a serious, credible discussion … to start building the trust we need to move forward. So far, they have given little reason for confidence. What is certain is that Iran's window to do so will not remain open forever."

We need to recognize an outcome of the meeting short of full verification of Iran's program means the window has been closed.

Various factors are motivating Ahmadinejad to possess nuclear weapons:

-- North Korea's successful development of such weapons despite vows by the United States to prevent it;

-- His belief Iran must be the dominant state in the Muslim world and; most worrisome;

-- His belief he is the chosen one -- personally selected by the Prophet Mohammed to be the catalyst for the return of the 12th Imam who, supposedly, will raise Islam to be the world's dominant religion.

Supposedly, the 12th Imam disappeared as a child in the ninth century and remains suspended in a state of occultation until his future return. Most Shiites say his return can only be triggered by world chaos that evolves naturally.

However, Ahmadinejad is a cultist who says man can cause that chaos. He promotes the belief he has been chosen by Mohammed. He claimed this was evident as an aura surrounded him when he spoke at the United Nations in 2005 (an aura apparently seen by no one but him), preventing listeners from blinking. He claims he has been visited by the 12th Imam.

We face a critical time. We can ill afford to misinterpret what a brazen Iranian leadership suggests is the fate awaiting the West. Earlier this year, a close adviser to the leadership warned, "The Americans have already been surprised (referring to 9/11), but the coming surprise will be very different."

There must be no mistake: What most non-Muslims fail to understand, except the Israelis, is Ahmadinejad is a mad man driven to possess nuclear weapons because he is hellbent on using them to usher in the 12th Imam's return.

Those still unconvinced about Ahmadinejad's intentions need to see the documentary he had produced laying out the events that will lead to the 12th Imam's return.

The aftermath of the upcoming meetings should make clear to the world that Ahmadinejad has crossed the Rubicon in regards to Iran's nuclear program. It can be expected he won't not allow full inspections to be conducted to determine Iran's true intentions. It is known he is undertaking certain clean-up operations at known sites, possibly to show them to inspectors simply as a ploy to buy additional time while production continues elsewhere.

When Caesar crossed the Rubicon, he aggressively moved forward to topple the Roman Republic and launch the Roman Empire. Ahmadinejad seeks to cross the Rubicon to topple Western democracies and launch, under the 12th Imam, an Islamic empire.

In Ahmadinejad's mind, the key to pulling this off is a nuclear weapon. The question remaining, therefore, is what the West will do when he crosses the point of no return to possess one.

(James. G. Zumwalt, is a retired U.S. Marine Corps officer who heads Admiral Zumwalt and Consultants, Inc. He is author of "Bare Feet, Iron Will -- Stories from the Other Side of Vietnam's Battlefields" and the recently released "Living the Juche Lie -- North Korea's Kim Dynasty.")

(United Press International's "Outside View" commentaries are written by outside contributors who specialize in a variety of important issues. The views expressed do not necessarily reflect those of United Press International. In the interests of creating an open forum, original submissions are invited.)