Why Ukraine trapped in this endless war?

Recent tension between Russia and Ukraine is not new as it's foundation was laid in late-2013 when Ukrainian Government rejected an association with European Union (EU) to build stronger relation with Russia.

November-December 2013

As President Yanukovych's cabinet abandons the agreement small protests started in Ukraine. Later in late November, at least 100000 people gathered to protest against this decision
In Early December, around 800000 people occupy Kiev City Hall and Independence Square.
In December only, Russian President Vladimir Putin gives an economic lifeline to Ukraine by agreeing to buy $15 Billion debt of Ukraine and Lower gas supplies price by 1/3rd.

January 2014

Deadly protest clashes arise between Security forces and Protesters. Protestors started attacking regional offices in Western Ukraine.

Then Prime- Minister Mykola Azarov resigns and Parliament declares the anti-protest law invalid.

February 2014

All protesters released, Kiev City Hall cleared.

Clashes erupt at Independence square.

 Then President Yanukovych signs compromise deal with opposition leaders.

Later in the month, Protestors take control of presidential administration building.

Then President disappears, Parliament votes to remove President from the Power.

Pro-Russian Groups captured the key building in Crimean Capital, Simferopol.

March 2014

Crimea's secession referendum to join Russia is backed by 97% of voters.

President Putin signs a bill to absorb Crimea into Russian territory.

April 2014

Protestors seized Government Buildings in East Ukranian cities of Donetsk, Luhansk, and Kharkiv demanding independence.

Acting President orders Military actions against Pro-Russian militants in the east.

May 2014

Pro-Russian Militants declared Donetsk and Luhansk independent.

Petro Poroshenko elected as President of Ukraine.

June 2014

Russian Parliament voted against Authorising the use of Russian Forces in Ukraine.

EU signs association agreement with Ukraine.

July 2014

Rebels abandon their Command center at Sloviansk.

EU and US imposes fresh sanctions on Russia.

August- November

Increased violence toward the south side of Donetsk. Russian Military is backing up Pro-Russians.

Ceasefire later restored in the region between Protestors and Ukrainian Army known as Security Zone

This region still remains one of the most intensified borders in the world as ceasefire violation is a common thing.

November 2018

3 Naval ships of Ukranian Navy was seized by Russia, Russia says that it violates Russian border near Crimea. Crew members were held prisoners by Russia.

December 2018

Ukraine imposes martial law on several parts of the country.

Ukraine bars Russian men aged 16-60 from an entry in Ukraine, limiting them to make the Pro-Russian private army like they did in 2014.

Ukraine increases their Army near borders, nuclear plants etc. 

To gain more knowledge on this topic you can watch VOX ATLAS youtube video