The Two Towers film is actually really impressive for how it feels like a cohesive story despite being about three groups of characters whose plotlines almost never intersect during the film’s runtime (Frodo/sam, Merry/Pippin, and Aragorn/Legolas/Gimli.)
Because the Fellowship almost never interacts with each other during the main plot, the filmmakers instead had to connect the plotlines thematically. Frodo/Sam never actually talk to Aragorn, but their plotlines mirror each other.
The Two Towers film is structured so that each splinter group of the Fellowship ultimately struggles with the same goal: they need to convince a despairing grief-stricken ally to aid in the war against Sauron. Theoden, Treebeard, and Faramir are all people who have suffered some great loss in the past wars. As a result, they are all set in their ways out of grief, and refuse to listen to the Fellowship’s advice or agree with their plans. (Until the very end.)
This is also where the films depart a lot from the source material. The two towers was probably the biggest adaptational challenge of the entire series, because the original book is split into two parts that focus on the POV of two different groups of characters (A Three Hunters book, and a Sam/Frodo book) — and then ends on a horrible cliffhanger. This works in the books but would not have worked on film at all.
The filmmakers’ attempts to build a Structured Film Story led to them emphasizing the idea of the Fellowship recruiting reluctant allies, and emphasizing the thematic idea of people being trapped within grief and stasis. Elrond predicts that the worst fate for Arwen would be to “linger on, in darkness and in doubt,” permanently frozen in grief; and this is the state we find most of the new characters in. Film!Theoden is portrayed as far more hesitant and grief-stricken than he was in the book, film!Treebeard is more reluctant and afraid of what war means for the Forest, and film!Faramir is more overwhelmed by the pressure to be like Boromir… and all three of them are overall far more heavily swayed by the Fellowship’s presence. (Though I still have beef with the way Faramir’s plotline was handled—XD) Because they needed to build out a structure that could work on film, they found this thematic throughline and really emphasized it.
Theoden’s grief over the death of his son makes him refuse the Fellowship’s advice to reach out to his allies or ride out against Saruman’s forces; Treebeard’s grief over the waning of the forest makes him decide that “he is on nobody’s side because nobody is on his side,” and Faramir’s grief over the death of Boromir makes him unwilling to try a solution that isn’t “what he believes Boromir would have done.”
These characters all start the film in a state of hopelessness and stasis and avoidance; then they’re ultimately forced to confront the source of their grief, and end the film by aiding the Fellowship.
This is also connected to the journey that all the Fellowship members need to go on. Frodo and Sam are forced to confront the grief at the idea that Frodo is being consumed by the Ring; Merry and Pippin have to face that “there won’t be a Shire” after Sauron’s victory; and Aragorn’s relationship with the people of Rohan forces him to confront his own fears about becoming a king and leading people to their death.
The plotlines are also really well connected through the use of music— like the Last March of the Ents leitmotif being used for Theoden’s choice to ride out against the Uruk-Hai, emphasizing the parallel between the way both characters have hesitated to “ride out and meet” the source of their grief.
And then Sam’s final speech, where a variation on the Shire leitmotif — (a version of the same variation that played in the end of Fellowship of the Ring)— becomes the final moment that ties all the disparate plot threads together. The film is centered on characters being overwhelmed by grief, and entering a state of numbness or stasis where they cut themselves off from the world. When this happens to Frodo, Sam encourages him to believes that there is still goodness in the world that’s worth fighting for— a culmination of all the ideas that have been built up throughout the past three hours.
Despite its flaws the film feels so cohesive, and the end of the film feels like such a satisfying resolution? Which is easy to take for granted because like, there were so many different moving pieces, and without a really clear thematic focus the film could’ve easily ended up falling apart.