US has called for regime change in Syria since at least 2011. US taxpayers have been forced to finance weapons for Syria regime change since at least 2012-AP 2011, NY Times 2012

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US wasn’t invited into Syria. Since at least 2011 US has said Syrian Pres. Assad “had to go.” Since at least 2012 US taxpayers have been forced to pay for weapons for bloody regime change in Syria. Syria would be completely justified in bombing the US:

June 21, 2012, “C.I.A. Said to Aid in Steering Arms to Syrian Opposition [Islamic terrorists],” NY Times, Eric Schmitt:

“The weapons, including automatic rifles, rocket-propelled grenades, ammunition and some antitank weapons, are being funneled mostly across the Turkish border by way of a shadowy network of intermediaries including Syria’s Muslim Brotherhood and paid for by Turkey, Saudi Arabia and Qatar, the officials said.”…
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Conversely, Russia was invited by the Syrian government in 2015 to help defend it:

9/30/2015, “Russia Begins Airstrikes In Syria After Assad’s Request,“ npr.org

Russia is a longtime Syrian ally.
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Added:

US created two “sides” in Syria: “Pentagon backed” forces and “CIA backed” forces. US taxpayers of course were forced to fund both “sides” which "repeatedly shot at each other":

3/27/2016, “In Syria, militias armed by the Pentagon fight those armed by the CIA,” LA Times, Nabih Bulos, W.J. Hennigan and Brian Bennett: 

“While the Pentagon’s actions are part of an overt effort by the U.S. and its allies against Islamic State, the CIA’s backing of [Islamic] militias is part of a separate covert U.S. effort aimed at keeping pressure on the Assad government in hopes of prodding the Syrian leader to the negotiating table….The fighting has intensified over the last two months, as CIA-armed units and Pentagon-armed ones have repeatedly shot at each other.”

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Added: Two years ago, Dec. 2016, without warmonger US at the table, Russia, Iran, and Turkey met to discuss peace in Syria:

12/20/2016, “Russia, Iran and Turkey push for Syria peace plan without US or UN,” Euronews.com

“After talks in Moscow, the three countries’ foreign ministers expressed confidence they could revive the stalled peace process. They also plan to try to expand a ceasefire.

The United States was notably absent from the meeting. Russia’s Foreign Minister Sergey Lavrov said: “Iran, Russian and Turkey express their readiness to act in favour and become guarantors of the agreement that is being prepared and negotiated at the moment by the Syrian government and opposition. The three call on all the other countries that have influence on the situation on the ground to do the same.”…The United States was notably absent from the meeting….

The US said that it was not worried about being left out of the discussion. A State Department spokesman said it welcomed any solutions that “lead to a reduction in bloodshed… whether or not we’re at the table”.

The move underlines the growing strength of Moscow’s links with Tehran and Ankara and reflects President Vladimir Putin’s desire to cement his country’s growing influence in the Middle East and more widely.

It also shows how fed up Russia is with what it sees as long and pointless talks with the [illegally invading] Obama administration over Syria. Foreign Minister Lavrov last week dismissed those talks as “fruitless sitting around”.

Russian Defence Minister Sergei Shoigu, who held parallel talks with his Iranian and Turkish opposite numbers, said afterwards:

“All previous attempts by the United States and its partners to agree on coordinated actions were doomed to failure. None of them wielded real influence over the situation on the ground.”
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Added: In 2011 US said Syria President Assad “had to go.” Why? The US has no business whatsoever meddling in the Middle East. US meddling there has been a complete disaster–unless the US goal was to clear a path for Islamic terrorists-they've succeeded in that:

Aug. 18, 2011, “Obama, allies call for ouster of Syria’s Assad,” AP

“In a statement released by the White House, Obama said Assad had lost all credibility as a leader and had to go….

“We have consistently said that President Assad must lead a democratic transition or get out of the way. He has not led. For the sake of the Syrian people, the time has come for President Assad to step aside.””

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