Merz's centre-right Christian Democrats (CDU) promised the region "flourishing landscapes" after the 1989 fall of the Berlin Wall led to national unification the following year.
But years of deindustrialisation, job losses and outward migration left deep scars that have aided the rise of the anti-immigration Alternative for Germany (AfD) party across the east.
After emerging as the second-biggest party in February's national elections, the AfD is now leading the polls in all five eastern states -- a serious threat for the CDU and its coalition allies.
"The AfD is continuing to gain ground in the east, and it seems clear that (Merz's) strategy of trying to stop the AfD is not working," Benjamin Hoehne, a political scientist at Chemnitz University of Technology, told AFP.
Merz needs to pay more attention to "the sensitivities and challenges in the east", he said.
In Saxony-Anhalt, set to hold regional elections in September 2026, AfD is polling on around 39 percent -- raising the possibility it could become the first German state to be led by an AfD government.
'Second-class citizens'Â
Today's eastern Germans feel like "second-class citizens", said Hans Vorlaender, a political science professor at Dresden University of Technology.
Merz, since taking office in early May, has only twice visited parts of the former East Germany outside Berlin.
Both trips were to military sites -- one in the port city of Rostock in Mecklenburg-Western Pomerania and the other in Brandenburg, the state that surrounds Berlin.
"He has been abroad a lot, then he was in North Rhine-Westphalia a lot, and now it would be nice if he came to Saxony or Brandenburg or Thuringia," Nora Seitz, a conservative member of parliament from Chemnitz, told AFP.
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On Thursday, Merz will attend a conference of Germany's eastern state leaders in the city of Weimar in Thuringia.
"The east has all the potential to develop further, but it is living with disappointed hopes. And restoring trust there will be a big task," Seitz said.
Many of those who took to the streets to demand the fall of the Berlin Wall "imagined everything differently" from what has actually turned out, she said.
"The majority of AfD voters in the east, in my opinion, are people who are simply disappointed in politics."
Many also see Merz as a "typical Wessi", Vorlaender said, using the region's slightly pejorative term for people from western Germany.
'Close ties with Russia'Â
Thursday's talks are expected to focus on energy, transport and efforts to boost the defence industry in the face of a hostile Russia.
But this is a sensitive topic in the former East Germany, where many people historically have "close ties with Russia", Seitz said.
Many older eastern Germans learned Russian in school or spent time studying in the Soviet Union, while others may have worked on infrastructure projects such as the Druzhba oil pipeline from Russia.
As Germany prepares to celebrate 35 years of reunification, differences still persist between the two halves of Germany.
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The east still lags behind in wealth and in areas such as industry and transport, though recent economic data has shown it is now outperforming the west in other areas.
Since 1990, five million people have left the east in search of a better life in western Germany.
"Demographic decline is preventing the state from maintaining local public services. Hospitals are closing, schools are closing, people feel abandoned," Hoehne said.
"That opens a window of opportunity for the AfD."
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