I heard about some ascetics who were incapable of concentrating their minds. After changing their environment, the Jhanas were realized easier.
Natural surroundings such as forests or jungles or the like might be more conducieve to meditation practice due to their natural tranquility. In Asia a lot of temples are purposely build in such places due to e.g. the calming effect they have on the mind. Natural surroundings also limit external reality and sense-inputs which is conducieve to introspection.
It might be more difficult (depending on the skill-level of the meditator) to cultivate Jhanas in a busy and hectic city environment or in a place that is torn apart by war and conflict.
Our surroundings do affect our ability to concentrate the mind. It is a fact that we are influenced by the environment. To get to the right mindset you can keep a Buddha statue in the meditation room. Or you could burn incense to give a pleasant odour conducive to meditation. These aromatic biotic materials which releases fragrant smoke when burned should be different to the ones that you use when going to a party. Perfumes that you use on an outing are a distraction, as they will arouse sense pleasures.
Bright colors, eye catching pictures, sensual fragrances, loud music, etc. create an environment for partying. A setting that is calm and peaceful, and conducive for contemplation is what you should try and create. Something in-between these two ends would be a large enough fireplace nook, with a built-in seat. Some dwellings have special niches, bay windows, breakfast nooks, seats built into the walls, walk-in-shelves, closets, sunken parts of the floor, or raised parts that can be turned into a special place for meditation purpose only. I’d do this than going out looking for an ideal place.
There’s an incident in Buddha’s time, where a monk was greatly attracted to a very serene and charming place in the forest and wanted very badly to meditate only there. Influenced by the environment he did not heed Buddha’s advice not to do so. When he went there and tried his utmost to focus his mind, he could not do so for any period of time. When he asked Buddha as to why it was so, Buddha said that in a previous birth he had many a sense pleasures at that very place. That was why unknowingly he was so attracted to this very place in this life.
To answer your question about adverse influences… it is good to be aware that this world is more complex that we think, and that we perceive only a tiny part of it. There is an unseen world that can influence us if ever we cross paths. “Seth Speaks” by Jane Roberts (1994) is a series of books based on “Seth”, a being who could “possess” her body with her permission. “Ramtha -The White Book” by J. Z. Knight (2005) is another book about a very benevolent being helping people to live a better life.
It is a good thing if the spirit world could help us on our Path, but if there are beings that are malevolent, how could we protect ourselves from such? Believe it or not… the best protection that you could have from such unseen forces is developing loving kindness to self and others. Spreading loving kindness to one and all whenever possible has many benefits. But what is most important is that it is like a double-sided sword that protects you from harm.
Only among beings in the lower five realms that you would find those who could be malevolent towards you. Those include one in this human world too. That is why it is good to keep your plans and intentions in this Dhamma Path very close to your heart, and share with only those that you look up to. Beings in the lowest four realms undergo unimaginable suffering, both physical and mental. If they could ever be able to influence you, they would rather hinder your progress than be of help to you.
When you spread metta, karuna, mudita, upekkha to such beings, what matters is not the particular set of words used, but what is felt in one’s heart. To do that one needs to truly comprehend that there is real suffering in this world, specially in the lower realms. While at it, be aware of what is “taken in” and what is “discarded”. Where there are thoughts of love, there cannot be any room for thoughts of fear. The most potent kusala citta that one could have is the “thought that arises with joy and wisdom automatically”. This thought gets stronger with increasing wisdom.
Because of the long samsara one had passed through, some places if one had frequently got through(for many rebirths) with unsurpassable worldly feeling/Tanha, it might be difficult for concentration. But only the Buddha know exactly all the being samsara and their attached Tahna. But it is not for every body. So generally it is not applicable for everybody (only in exceptional case). The same applied to past work habit, food fondness etc. The most important thing is to relentlessly work hard toward nibbana following the Buddha teaching.
To get into Jhana you have to pass through vitakka and vicara which is sustained and applied though on an object. Even if you have higher Jhana many (except for very accomplished meditators) have to pass through each applied and sustained thoughts.
When there is disturbances in the environment it is very hard to have sustained thought, hence in ability to get into Jhana. More the time you have to spend getting in the Jhana more environment will have a bearing as then you are developing applied and sustained thought you might get disturbed.
When the environment is more tranquil, then applied and sustained thought becomes possible and easier (no distractions) where by you can enter the Jhana.
AN 10.99 Upali Sutta might be related to your question. Buddha told Ven Upila when he was not yet an Arahat that secluded forest is not a place for those who have not had a concentrated mind.
Upali, life in forest dwellings and jungle paths is difficult to bear. It is difficult to be attached to seclusion. The mind of the bhikkhu who is not concentrated is carried away by solitude. Upali, if someone says: I will abide in jungle forests to gain concentration. He could expect a sinking down or an elation..
Ven Upali was one of the top Buddha's principle disciples master of vinaya