Why did Rome and Byzantium fall apart after centuries of success? What causes civilizations to collapse, from a dysfunctional fourth-century-B.C. Athens to contemporary bankrupt Greece?

The answer is usually not enemies at the gates, but the pathologies inside them.

What ruins societies is well known: too much consumption and not enough production, a debased currency, and endemic corruption.

Americans currently deal with all those symptoms. But two more fundamental causes for decline are even more frightening: an unwillingness to pay taxes and the end of the rule of law.

Al Sharpton is again prominently in the news, blaming various groups for the Baltimore unrest. But Sharpton currently owes the U.S. government more than $3 million in back taxes, according to reports. His excuses have ranged from insufficient funds to pay them to sloppy record-keeping and mysterious fires.

Sharpton, a frequent White House guest, apparently assumes that his community-organizing provides him political exemption from federal tax law. He seems to be right, at least as long as the current administration is in power.

The Clinton Foundation is expected to refile its tax returns for 2010, 2011 and 2012 after failing to separate government grants from donations. If an average citizen tried to amend his taxes for such huge sums and from that long ago, he would probably be under indictment.

News reports of undocumented donations from foreign governments caught the foundation underreporting its income. The well-connected Clinton clan apparently had assumed that their political status ensured them immunity.

In the current political landscape, ideology also offers cover for tax noncompliance. Two of the most liberal talking heads at the MSNBC cable news network, Touré Neblett and Melissa Harris-Perry, known for their advocacy of higher tax rates on the affluent, turn out to be both quite well off and quite unwilling to pay their fair share of taxes. Reports indicate that Neblett and Harris-Perry both owe more than $50,000 in delinquent taxes.

Who will police the tax police?

Former IRS official Lois Lerner and her subordinates were found to have targeted conservative nonprofit groups for excessive federal scrutiny. While testifying before Congress, Lerner invoked her Fifth Amendment right against self-incrimination, and investigators later found that two years of her emails had gone missing in a mysterious computer crash. Lerner has not been charged.

Under the current system, the very wealthy have the pull and capital to navigate around the 3.7-million-word IRS tax code. Billionaire George Soros, a proponent of big government and higher taxes, reportedly could face a tax bill of approximately $7 billion after years of deferrals.

Nonparticipation in the tax system and noncompliance are recipes for social and cultural disaster — as we see with the current climbing tax rates, huge deficits and unsustainable national debt.

Our laws are becoming as politicized as our tax system.

Whatever one thinks of illegal immigration, it’s undeniable that under the Obama administration, federal immigration law enforcement is now predicated on politics. The law as it was written suddenly has ceased to exist — at least for particular groups at particular times and places.

In the last six years, the enforcement of federal laws has depended on their apparent political utility. If elements of the controversial Affordable Care Act were deemed politically risky, then their implementation was ignored until after an election. If the Environmental Protection Agency could not see its agenda passed through Congress as federal law, then it implemented its green policies by fiat.

If the Obama administration reaches a controversial agreement with Iran that will not meet the Constitutional test of ratification by two-thirds of the Senate, then it will not be called a treaty and instead be imposed by presidential executive order.

Prosecutors have never been more ideologically driven. Sen. Bob Menendez (D-N.J.) opposes administration policies on Cuba and Iran — and then suddenly faces federal indictments on charges covering a period from 2006 to 2013.

In the tragic Freddie Gray case, Baltimore State’s Attorney Marilyn Mosby all but assured an angry crowd that she had provided them indictments for murder and manslaughter and thereby expected calm in the streets in return. She indicted six Baltimore policemen on charges that are likely to be reduced or disproved in court, but those charges served the short-term purpose of defusing unchecked rioting and looting. Warping the law was thought to be more effective in easing tensions than enforcing it.

Increasingly in the United States, the degree to which a law is enforced — or whether a person is indicted — depends on political considerations. But when citizens do not pay any income taxes, or choose not to pay taxes that they owe and expect impunity, a complex society unwinds.

And when the law has becomes negotiable, civilization utterly collapses.

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