DONALD TRUMP PROMISED that his State of the Union address would focus on “unification.” But Trump advocating national unity is like a pyromaniac promoting lighter fluids. His goal is and has always been disunion.

The man thrives on divisiveness. It’s how he keeps himself the center of attention, fuels his base and ensures that no matter what facts are revealed about him, his followers will stick by him.

There’s another reason Trump has aimed to divide and why he continuously pours salt into the nation’s deepest wounds over ethnicity, immigration, race and gender.

He wants to divert attention from the biggest and most threatening divide of all: the widening imbalance of wealth and power between the vast majority, who have little or none, and a tiny minority, who are accumulating just about all.

“Divide and conquer” is one of the oldest strategies in the demagogic playbook. Keep the public angry at each other so they don’t unite against those who are running off with the goods.

Over the last four decades, while the median wage has barely budged, the incomes of the richest 0.1% have increased by more than 300% and the incomes of the top 0.001% (the 2,300 richest Americans) have soared by more than 600%. The net worth of the wealthiest 0.1% of Americans now almost equals that of the bottom 90% combined.

This grotesque imbalance is undermining American democracy.

“The preferences of the average American appear to have only a miniscule, near-zero, statistically nonsignificant impact upon public policy,” concluded Princeton University’s Martin Gilens and Northwestern University’s Benjamin Page a few years ago, after analyzing in detail 1,799 policy issues that came before Congress. Lawmakers respond instead to the demands of wealthy individuals and moneyed business interests.

No secret there. In fact, Trump campaigned as a populist, exploiting the public’s justifiable sense that the game is rigged against them.

But he never attacked the American oligarchy and his divide and conquer strategy as president has disguised his efforts to make the oligarchy even stronger.

His tax cuts; his evisceration of labor laws; his filling of Cabinet and sub-Cabinet positions with corporate shills; and his rollbacks of health, safety, environmental and financial regulations have made the super rich far richer at the expense of average Americans.

Meanwhile, he and his fellow Republicans continue to suppress votes.

Senate Republican leader Mitch McConnell has denounced Democratic proposals to increase voter turnout, even calling the idea of making Election Day a federal holiday a power grab. Of course, it’s a power grab, for the people.

Sitting behind Trump for his State of the Union address will be Nancy Pelosi, the formidable speaker of the house who refused to blink when Trump closed the U.S. government in order to fund his wall at the Mexican border.

Has Trump met his match in Pelosi? The real question is whether and to what extent Pelosi and other Democrats also will unblinkingly take on America’s increasing concentration of wealth and power.

In recent weeks, Sens. Elizabeth Warren and Bernie Sanders — both eyeing presidential bids — have, along with 29-year-old freshman Rep. Alexandria Ocasio-Cortez, called for sharp increases in taxes on the super rich.

Some Democratic presidential hopefuls also are proposing to expand access to health insurance by creating Medicare for all.

Polls show strong public support, but the corporate Democrats who still bankroll much of the party are not happy with this drift to the putative “left.”

Michael Bloomberg, the billionaire former New York mayor now considering a presidential run as a Democrat, warned that when you try to redistribute wealth you get “Venezuela.” Howard Schultz, the billionaire former Starbucks CEO who is considering an independent presidential bid, called Warren’s plan ridiculous.

Trump, along with the Republicans and perhaps, some corporate Democrats, would rather opponents focus on the same ethnic, racial and gender differences he uses to divide and conquer.

But Democratic leaders and candidates appear to understand that the largest threat to the state of the union — one that trumps all others, rendering it all but impossible to address anything else — is the deepening divide of wealth and power between the many and the few.

Robert Reich’s latest book is “The Common Good” and his newest documentary is “Saving Capitalism.”